SMTPD(8) SMTPD(8)
NAME
smtpd - Postfix SMTP server
SYNOPSIS
smtpd [generic Postfix daemon options]
sendmail -bs
DESCRIPTION
The SMTP server accepts network connection requests and performs zero
or more SMTP transactions per connection. Each received message is
piped through the cleanup(8) daemon, and is placed into the incoming
queue as one single queue file. For this mode of operation, the pro-
gram expects to be run from the master(8) process manager.
Alternatively, the SMTP server be can run in stand-alone mode; this is
traditionally obtained with "sendmail -bs". When the SMTP server runs
stand-alone with non $mail_owner privileges, it receives mail even
while the mail system is not running, deposits messages directly into
the maildrop queue, and disables the SMTP server's access policies. As
of Postfix version 2.3, the SMTP server refuses to receive mail from
the network when it runs with non $mail_owner privileges.
The SMTP server implements a variety of policies for connection
requests, and for parameters given to HELO, ETRN, MAIL FROM, VRFY and
RCPT TO commands. They are detailed below and in the main.cf configura-
tion file.
SECURITY
The SMTP server is moderately security-sensitive. It talks to SMTP
clients and to DNS servers on the network. The SMTP server can be run
chrooted at fixed low privilege.
STANDARDS
RFC 821 (SMTP protocol)
RFC 1123 (Host requirements)
RFC 1652 (8bit-MIME transport)
RFC 1869 (SMTP service extensions)
RFC 1870 (Message size declaration)
RFC 1985 (ETRN command)
RFC 2034 (SMTP enhanced status codes)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2920 (SMTP pipelining)
RFC 3207 (STARTTLS command)
RFC 3461 (SMTP DSN extension)
RFC 3463 (Enhanced status codes)
RFC 3848 (ESMTP transmission types)
RFC 4409 (Message submission)
RFC 4954 (AUTH command)
RFC 5321 (SMTP protocol)
RFC 6531 (Internationalized SMTP)
RFC 6533 (Internationalized Delivery Status Notifications)
RFC 7505 ("Null MX" No Service Resource Record)
DIAGNOSTICS
Problems and transactions are logged to syslogd(8).
Depending on the setting of the notify_classes parameter, the postmas-
ter is notified of bounces, protocol problems, policy violations, and
of other trouble.
CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically, as smtpd(8) processes
run for only a limited amount of time. Use the command "postfix reload"
to speed up a change.
The text below provides only a parameter summary. See postconf(5) for
more details including examples.
COMPATIBILITY CONTROLS
The following parameters work around implementation errors in other
software, and/or allow you to override standards in order to prevent
undesirable use.
broken_sasl_auth_clients (no)
Enable interoperability with remote SMTP clients that implement
an obsolete version of the AUTH command (RFC 4954).
disable_vrfy_command (no)
Disable the SMTP VRFY command.
smtpd_noop_commands (empty)
List of commands that the Postfix SMTP server replies to with
"250 Ok", without doing any syntax checks and without changing
state.
strict_rfc821_envelopes (no)
Require that addresses received in SMTP MAIL FROM and RCPT TO
commands are enclosed with <>, and that those addresses do not
contain RFC 822 style comments or phrases.
Available in Postfix version 2.1 and later:
smtpd_reject_unlisted_sender (no)
Request that the Postfix SMTP server rejects mail from unknown
sender addresses, even when no explicit reject_unlisted_sender
access restriction is specified.
smtpd_sasl_exceptions_networks (empty)
What remote SMTP clients the Postfix SMTP server will not offer
AUTH support to.
Available in Postfix version 2.2 and later:
smtpd_discard_ehlo_keyword_address_maps (empty)
Lookup tables, indexed by the remote SMTP client address, with
case insensitive lists of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP server will not send in the
EHLO response to a remote SMTP client.
smtpd_discard_ehlo_keywords (empty)
A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP server will not send in the
EHLO response to a remote SMTP client.
smtpd_delay_open_until_valid_rcpt (yes)
Postpone the start of an SMTP mail transaction until a valid
RCPT TO command is received.
Available in Postfix version 2.3 and later:
smtpd_tls_always_issue_session_ids (yes)
Force the Postfix SMTP server to issue a TLS session id, even
when TLS session caching is turned off (smtpd_tls_ses-
sion_cache_database is empty).
Available in Postfix version 2.6 and later:
tcp_windowsize (0)
An optional workaround for routers that break TCP window scal-
ing.
Available in Postfix version 2.7 and later:
smtpd_command_filter (empty)
A mechanism to transform commands from remote SMTP clients.
Available in Postfix version 2.9 and later:
smtpd_per_record_deadline (normal: no, overload: yes)
Change the behavior of the smtpd_timeout and smtpd_start-
tls_timeout time limits, from a time limit per read or write
system call, to a time limit to send or receive a complete
record (an SMTP command line, SMTP response line, SMTP message
content line, or TLS protocol message).
Available in Postfix version 3.0 and later:
smtpd_dns_reply_filter (empty)
Optional filter for Postfix SMTP server DNS lookup results.
ADDRESS REWRITING CONTROLS
See the ADDRESS_REWRITING_README document for a detailed discussion of
Postfix address rewriting.
receive_override_options (empty)
Enable or disable recipient validation, built-in content filter-
ing, or address mapping.
Available in Postfix version 2.2 and later:
local_header_rewrite_clients (permit_inet_interfaces)
Rewrite message header addresses in mail from these clients and
update incomplete addresses with the domain name in $myorigin or
$mydomain; either don't rewrite message headers from other
clients at all, or rewrite message headers and update incomplete
addresses with the domain specified in the remote_header_re-
write_domain parameter.
BEFORE-SMTPD PROXY AGENT
Available in Postfix version 2.10 and later:
smtpd_upstream_proxy_protocol (empty)
The name of the proxy protocol used by an optional before-smtpd
proxy agent.
smtpd_upstream_proxy_timeout (5s)
The time limit for the proxy protocol specified with the
smtpd_upstream_proxy_protocol parameter.
AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 1.0, Postfix can be configured to send new mail to an
external content filter AFTER the mail is queued. This content filter
is expected to inject mail back into a (Postfix or other) MTA for fur-
ther delivery. See the FILTER_README document for details.
content_filter (empty)
After the message is queued, send the entire message to the
specified transport:destination.
BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 2.1, the Postfix SMTP server can be configured to send
incoming mail to a real-time SMTP-based content filter BEFORE mail is
queued. This content filter is expected to inject mail back into Post-
fix. See the SMTPD_PROXY_README document for details on how to config-
ure and operate this feature.
smtpd_proxy_filter (empty)
The hostname and TCP port of the mail filtering proxy server.
smtpd_proxy_ehlo ($myhostname)
How the Postfix SMTP server announces itself to the proxy fil-
ter.
smtpd_proxy_options (empty)
List of options that control how the Postfix SMTP server commu-
nicates with a before-queue content filter.
smtpd_proxy_timeout (100s)
The time limit for connecting to a proxy filter and for sending
or receiving information.
BEFORE QUEUE MILTER CONTROLS
As of version 2.3, Postfix supports the Sendmail version 8 Milter (mail
filter) protocol. These content filters run outside Postfix. They can
inspect the SMTP command stream and the message content, and can
request modifications before mail is queued. For details see the MIL-
TER_README document.
smtpd_milters (empty)
A list of Milter (mail filter) applications for new mail that
arrives via the Postfix smtpd(8) server.
milter_protocol (6)
The mail filter protocol version and optional protocol exten-
sions for communication with a Milter application; prior to
Postfix 2.6 the default protocol is 2.
milter_default_action (tempfail)
The default action when a Milter (mail filter) application is
unavailable or mis-configured.
milter_macro_daemon_name ($myhostname)
The {daemon_name} macro value for Milter (mail filter) applica-
tions.
milter_macro_v ($mail_name $mail_version)
The {v} macro value for Milter (mail filter) applications.
milter_connect_timeout (30s)
The time limit for connecting to a Milter (mail filter) applica-
tion, and for negotiating protocol options.
milter_command_timeout (30s)
The time limit for sending an SMTP command to a Milter (mail
filter) application, and for receiving the response.
milter_content_timeout (300s)
The time limit for sending message content to a Milter (mail
filter) application, and for receiving the response.
milter_connect_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after completion of an SMTP connection.
milter_helo_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after the SMTP HELO or EHLO command.
milter_mail_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after the SMTP MAIL FROM command.
milter_rcpt_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after the SMTP RCPT TO command.
milter_data_macros (see 'postconf -d' output)
The macros that are sent to version 4 or higher Milter (mail
filter) applications after the SMTP DATA command.
milter_unknown_command_macros (see 'postconf -d' output)
The macros that are sent to version 3 or higher Milter (mail
filter) applications after an unknown SMTP command.
milter_end_of_header_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after the end of the message header.
milter_end_of_data_macros (see 'postconf -d' output)
The macros that are sent to Milter (mail filter) applications
after the message end-of-data.
Available in Postfix version 3.1 and later:
milter_macro_defaults (empty)
Optional list of name=value pairs that specify default values
for arbitrary macros that Postfix may send to Milter applica-
tions.
Available in Postfix version 3.2 and later:
smtpd_milter_maps (empty)
Lookup tables with Milter settings per remote SMTP client IP
address.
GENERAL CONTENT INSPECTION CONTROLS
The following parameters are applicable for both built-in and external
content filters.
Available in Postfix version 2.1 and later:
receive_override_options (empty)
Enable or disable recipient validation, built-in content filter-
ing, or address mapping.
EXTERNAL CONTENT INSPECTION CONTROLS
The following parameters are applicable for both before-queue and
after-queue content filtering.
Available in Postfix version 2.1 and later:
smtpd_authorized_xforward_hosts (empty)
What remote SMTP clients are allowed to use the XFORWARD fea-
ture.
SASL AUTHENTICATION CONTROLS
Postfix SASL support (RFC 4954) can be used to authenticate remote SMTP
clients to the Postfix SMTP server, and to authenticate the Postfix
SMTP client to a remote SMTP server. See the SASL_README document for
details.
broken_sasl_auth_clients (no)
Enable interoperability with remote SMTP clients that implement
an obsolete version of the AUTH command (RFC 4954).
smtpd_sasl_auth_enable (no)
Enable SASL authentication in the Postfix SMTP server.
smtpd_sasl_local_domain (empty)
The name of the Postfix SMTP server's local SASL authentication
realm.
smtpd_sasl_security_options (noanonymous)
Postfix SMTP server SASL security options; as of Postfix 2.3 the
list of available features depends on the SASL server implemen-
tation that is selected with smtpd_sasl_type.
smtpd_sender_login_maps (empty)
Optional lookup table with the SASL login names that own the
sender (MAIL FROM) addresses.
Available in Postfix version 2.1 and later:
smtpd_sasl_exceptions_networks (empty)
What remote SMTP clients the Postfix SMTP server will not offer
AUTH support to.
Available in Postfix version 2.1 and 2.2:
smtpd_sasl_application_name (smtpd)
The application name that the Postfix SMTP server uses for SASL
server initialization.
Available in Postfix version 2.3 and later:
smtpd_sasl_authenticated_header (no)
Report the SASL authenticated user name in the smtpd(8) Received
message header.
smtpd_sasl_path (smtpd)
Implementation-specific information that the Postfix SMTP server
passes through to the SASL plug-in implementation that is
selected with smtpd_sasl_type.
smtpd_sasl_type (cyrus)
The SASL plug-in type that the Postfix SMTP server should use
for authentication.
Available in Postfix version 2.5 and later:
cyrus_sasl_config_path (empty)
Search path for Cyrus SASL application configuration files, cur-
rently used only to locate the $smtpd_sasl_path.conf file.
Available in Postfix version 2.11 and later:
smtpd_sasl_service (smtp)
The service name that is passed to the SASL plug-in that is
selected with smtpd_sasl_type and smtpd_sasl_path.
STARTTLS SUPPORT CONTROLS
Detailed information about STARTTLS configuration may be found in the
TLS_README document.
smtpd_tls_security_level (empty)
The SMTP TLS security level for the Postfix SMTP server; when a
non-empty value is specified, this overrides the obsolete param-
eters smtpd_use_tls and smtpd_enforce_tls.
smtpd_sasl_tls_security_options ($smtpd_sasl_security_options)
The SASL authentication security options that the Postfix SMTP
server uses for TLS encrypted SMTP sessions.
smtpd_starttls_timeout (see 'postconf -d' output)
The time limit for Postfix SMTP server write and read operations
during TLS startup and shutdown handshake procedures.
smtpd_tls_CAfile (empty)
A file containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or inter-
mediate CA certificates.
smtpd_tls_CApath (empty)
A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or inter-
mediate CA certificates.
smtpd_tls_always_issue_session_ids (yes)
Force the Postfix SMTP server to issue a TLS session id, even
when TLS session caching is turned off (smtpd_tls_ses-
sion_cache_database is empty).
smtpd_tls_ask_ccert (no)
Ask a remote SMTP client for a client certificate.
smtpd_tls_auth_only (no)
When TLS encryption is optional in the Postfix SMTP server, do
not announce or accept SASL authentication over unencrypted con-
nections.
smtpd_tls_ccert_verifydepth (9)
The verification depth for remote SMTP client certificates.
smtpd_tls_cert_file (empty)
File with the Postfix SMTP server RSA certificate in PEM format.
smtpd_tls_exclude_ciphers (empty)
List of ciphers or cipher types to exclude from the SMTP server
cipher list at all TLS security levels.
smtpd_tls_dcert_file (empty)
File with the Postfix SMTP server DSA certificate in PEM format.
smtpd_tls_dh1024_param_file (empty)
File with DH parameters that the Postfix SMTP server should use
with non-export EDH ciphers.
smtpd_tls_dh512_param_file (empty)
File with DH parameters that the Postfix SMTP server should use
with export-grade EDH ciphers.
smtpd_tls_dkey_file ($smtpd_tls_dcert_file)
File with the Postfix SMTP server DSA private key in PEM format.
smtpd_tls_key_file ($smtpd_tls_cert_file)
File with the Postfix SMTP server RSA private key in PEM format.
smtpd_tls_loglevel (0)
Enable additional Postfix SMTP server logging of TLS activity.
smtpd_tls_mandatory_ciphers (medium)
The minimum TLS cipher grade that the Postfix SMTP server will
use with mandatory TLS encryption.
smtpd_tls_mandatory_exclude_ciphers (empty)
Additional list of ciphers or cipher types to exclude from the
Postfix SMTP server cipher list at mandatory TLS security lev-
els.
smtpd_tls_mandatory_protocols (!SSLv2, !SSLv3)
The SSL/TLS protocols accepted by the Postfix SMTP server with
mandatory TLS encryption.
smtpd_tls_received_header (no)
Request that the Postfix SMTP server produces Received: message
headers that include information about the protocol and cipher
used, as well as the remote SMTP client CommonName and client
certificate issuer CommonName.
smtpd_tls_req_ccert (no)
With mandatory TLS encryption, require a trusted remote SMTP
client certificate in order to allow TLS connections to proceed.
smtpd_tls_wrappermode (no)
Run the Postfix SMTP server in the non-standard "wrapper" mode,
instead of using the STARTTLS command.
tls_daemon_random_bytes (32)
The number of pseudo-random bytes that an smtp(8) or smtpd(8)
process requests from the tlsmgr(8) server in order to seed its
internal pseudo random number generator (PRNG).
tls_high_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "high" grade ciphers.
tls_medium_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "medium" or higher grade ciphers.
tls_low_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "low" or higher grade ciphers.
tls_export_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "export" or higher grade ciphers.
tls_null_cipherlist (eNULL:!aNULL)
The OpenSSL cipherlist for "NULL" grade ciphers that provide
authentication without encryption.
Available in Postfix version 2.5 and later:
smtpd_tls_fingerprint_digest (md5)
The message digest algorithm to construct remote SMTP
client-certificate fingerprints or public key fingerprints
(Postfix 2.9 and later) for check_ccert_access and per-
mit_tls_clientcerts.
Available in Postfix version 2.6 and later:
smtpd_tls_protocols (!SSLv2, !SSLv3)
List of TLS protocols that the Postfix SMTP server will exclude
or include with opportunistic TLS encryption.
smtpd_tls_ciphers (medium)
The minimum TLS cipher grade that the Postfix SMTP server will
use with opportunistic TLS encryption.
smtpd_tls_eccert_file (empty)
File with the Postfix SMTP server ECDSA certificate in PEM for-
mat.
smtpd_tls_eckey_file ($smtpd_tls_eccert_file)
File with the Postfix SMTP server ECDSA private key in PEM for-
mat.
smtpd_tls_eecdh_grade (see 'postconf -d' output)
The Postfix SMTP server security grade for ephemeral ellip-
tic-curve Diffie-Hellman (EECDH) key exchange.
tls_eecdh_strong_curve (prime256v1)
The elliptic curve used by the Postfix SMTP server for sensibly
strong ephemeral ECDH key exchange.
tls_eecdh_ultra_curve (secp384r1)
The elliptic curve used by the Postfix SMTP server for maximally
strong ephemeral ECDH key exchange.
Available in Postfix version 2.8 and later:
tls_preempt_cipherlist (no)
With SSLv3 and later, use the Postfix SMTP server's cipher pref-
erence order instead of the remote client's cipher preference
order.
tls_disable_workarounds (see 'postconf -d' output)
List or bit-mask of OpenSSL bug work-arounds to disable.
Available in Postfix version 2.11 and later:
tlsmgr_service_name (tlsmgr)
The name of the tlsmgr(8) service entry in master.cf.
Available in Postfix version 3.0 and later:
tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0:
aes-128-cbc)
Algorithm used to encrypt RFC5077 TLS session tickets.
Available in Postfix version 3.2 and later:
tls_eecdh_auto_curves (see 'postconf -d' output)
The prioritized list of elliptic curves supported by the Postfix
SMTP client and server.
OBSOLETE STARTTLS CONTROLS
The following configuration parameters exist for compatibility with
Postfix versions before 2.3. Support for these will be removed in a
future release.
smtpd_use_tls (no)
Opportunistic TLS: announce STARTTLS support to remote SMTP
clients, but do not require that clients use TLS encryption.
smtpd_enforce_tls (no)
Mandatory TLS: announce STARTTLS support to remote SMTP clients,
and require that clients use TLS encryption.
smtpd_tls_cipherlist (empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS
cipher list.
SMTPUTF8 CONTROLS
Preliminary SMTPUTF8 support is introduced with Postfix 3.0.
smtputf8_enable (yes)
Enable preliminary SMTPUTF8 support for the protocols described
in RFC 6531..6533.
strict_smtputf8 (no)
Enable stricter enforcement of the SMTPUTF8 protocol.
smtputf8_autodetect_classes (sendmail, verify)
Detect that a message requires SMTPUTF8 support for the speci-
fied mail origin classes.
Available in Postfix version 3.2 and later:
enable_idna2003_compatibility (no)
Enable 'transitional' compatibility between IDNA2003 and
IDNA2008, when converting UTF-8 domain names to/from the ASCII
form that is used for DNS lookups.
VERP SUPPORT CONTROLS
With VERP style delivery, each recipient of a message receives a cus-
tomized copy of the message with his/her own recipient address encoded
in the envelope sender address. The VERP_README file describes config-
uration and operation details of Postfix support for variable envelope
return path addresses. VERP style delivery is requested with the SMTP
XVERP command or with the "sendmail -V" command-line option and is
available in Postfix version 1.1 and later.
default_verp_delimiters (+=)
The two default VERP delimiter characters.
verp_delimiter_filter (-=+)
The characters Postfix accepts as VERP delimiter characters on
the Postfix sendmail(1) command line and in SMTP commands.
Available in Postfix version 1.1 and 2.0:
authorized_verp_clients ($mynetworks)
What remote SMTP clients are allowed to specify the XVERP com-
mand.
Available in Postfix version 2.1 and later:
smtpd_authorized_verp_clients ($authorized_verp_clients)
What remote SMTP clients are allowed to specify the XVERP com-
mand.
TROUBLE SHOOTING CONTROLS
The DEBUG_README document describes how to debug parts of the Postfix
mail system. The methods vary from making the software log a lot of
detail, to running some daemon processes under control of a call tracer
or debugger.
debug_peer_level (2)
The increment in verbose logging level when a remote client or
server matches a pattern in the debug_peer_list parameter.
debug_peer_list (empty)
Optional list of remote client or server hostname or network
address patterns that cause the verbose logging level to
increase by the amount specified in $debug_peer_level.
error_notice_recipient (postmaster)
The recipient of postmaster notifications about mail delivery
problems that are caused by policy, resource, software or proto-
col errors.
internal_mail_filter_classes (empty)
What categories of Postfix-generated mail are subject to
before-queue content inspection by non_smtpd_milters,
header_checks and body_checks.
notify_classes (resource, software)
The list of error classes that are reported to the postmaster.
smtpd_reject_footer (empty)
Optional information that is appended after each Postfix SMTP
server 4XX or 5XX response.
soft_bounce (no)
Safety net to keep mail queued that would otherwise be returned
to the sender.
Available in Postfix version 2.1 and later:
smtpd_authorized_xclient_hosts (empty)
What remote SMTP clients are allowed to use the XCLIENT feature.
Available in Postfix version 2.10 and later:
smtpd_log_access_permit_actions (empty)
Enable logging of the named "permit" actions in SMTP server
access lists (by default, the SMTP server logs "reject" actions
but not "permit" actions).
KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS
As of Postfix version 2.0, the SMTP server rejects mail for unknown
recipients. This prevents the mail queue from clogging up with undeliv-
erable MAILER-DAEMON messages. Additional information on this topic is
in the LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents.
show_user_unknown_table_name (yes)
Display the name of the recipient table in the "User unknown"
responses.
canonical_maps (empty)
Optional address mapping lookup tables for message headers and
envelopes.
recipient_canonical_maps (empty)
Optional address mapping lookup tables for envelope and header
recipient addresses.
sender_canonical_maps (empty)
Optional address mapping lookup tables for envelope and header
sender addresses.
Parameters concerning known/unknown local recipients:
mydestination ($myhostname, localhost.$mydomain, localhost)
The list of domains that are delivered via the $local_transport
mail delivery transport.
inet_interfaces (all)
The network interface addresses that this mail system receives
mail on.
proxy_interfaces (empty)
The network interface addresses that this mail system receives
mail on by way of a proxy or network address translation unit.
inet_protocols (all)
The Internet protocols Postfix will attempt to use when making
or accepting connections.
local_recipient_maps (proxy:unix:passwd.byname $alias_maps)
Lookup tables with all names or addresses of local recipients: a
recipient address is local when its domain matches $mydestina-
tion, $inet_interfaces or $proxy_interfaces.
unknown_local_recipient_reject_code (550)
The numerical Postfix SMTP server response code when a recipient
address is local, and $local_recipient_maps specifies a list of
lookup tables that does not match the recipient.
Parameters concerning known/unknown recipients of relay destinations:
relay_domains (Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)
What destination domains (and subdomains thereof) this system
will relay mail to.
relay_recipient_maps (empty)
Optional lookup tables with all valid addresses in the domains
that match $relay_domains.
unknown_relay_recipient_reject_code (550)
The numerical Postfix SMTP server reply code when a recipient
address matches $relay_domains, and relay_recipient_maps speci-
fies a list of lookup tables that does not match the recipient
address.
Parameters concerning known/unknown recipients in virtual alias
domains:
virtual_alias_domains ($virtual_alias_maps)
Postfix is final destination for the specified list of virtual
alias domains, that is, domains for which all addresses are
aliased to addresses in other local or remote domains.
virtual_alias_maps ($virtual_maps)
Optional lookup tables that alias specific mail addresses or
domains to other local or remote address.
unknown_virtual_alias_reject_code (550)
The Postfix SMTP server reply code when a recipient address
matches $virtual_alias_domains, and $virtual_alias_maps speci-
fies a list of lookup tables that does not match the recipient
address.
Parameters concerning known/unknown recipients in virtual mailbox
domains:
virtual_mailbox_domains ($virtual_mailbox_maps)
Postfix is final destination for the specified list of domains;
mail is delivered via the $virtual_transport mail delivery
transport.
virtual_mailbox_maps (empty)
Optional lookup tables with all valid addresses in the domains
that match $virtual_mailbox_domains.
unknown_virtual_mailbox_reject_code (550)
The Postfix SMTP server reply code when a recipient address
matches $virtual_mailbox_domains, and $virtual_mailbox_maps
specifies a list of lookup tables that does not match the recip-
ient address.
RESOURCE AND RATE CONTROLS
The following parameters limit resource usage by the SMTP server and/or
control client request rates.
line_length_limit (2048)
Upon input, long lines are chopped up into pieces of at most
this length; upon delivery, long lines are reconstructed.
queue_minfree (0)
The minimal amount of free space in bytes in the queue file sys-
tem that is needed to receive mail.
message_size_limit (10240000)
The maximal size in bytes of a message, including envelope
information.
smtpd_recipient_limit (1000)
The maximal number of recipients that the Postfix SMTP server
accepts per message delivery request.
smtpd_timeout (normal: 300s, overload: 10s)
The time limit for sending a Postfix SMTP server response and
for receiving a remote SMTP client request.
smtpd_history_flush_threshold (100)
The maximal number of lines in the Postfix SMTP server command
history before it is flushed upon receipt of EHLO, RSET, or end
of DATA.
Available in Postfix version 2.3 and later:
smtpd_peername_lookup (yes)
Attempt to look up the remote SMTP client hostname, and verify
that the name matches the client IP address.
The per SMTP client connection count and request rate limits are imple-
mented in co-operation with the anvil(8) service, and are available in
Postfix version 2.2 and later.
smtpd_client_connection_count_limit (50)
How many simultaneous connections any client is allowed to make
to this service.
smtpd_client_connection_rate_limit (0)
The maximal number of connection attempts any client is allowed
to make to this service per time unit.
smtpd_client_message_rate_limit (0)
The maximal number of message delivery requests that any client
is allowed to make to this service per time unit, regardless of
whether or not Postfix actually accepts those messages.
smtpd_client_recipient_rate_limit (0)
The maximal number of recipient addresses that any client is
allowed to send to this service per time unit, regardless of
whether or not Postfix actually accepts those recipients.
smtpd_client_event_limit_exceptions ($mynetworks)
Clients that are excluded from smtpd_client_*_count/rate_limit
restrictions.
Available in Postfix version 2.3 and later:
smtpd_client_new_tls_session_rate_limit (0)
The maximal number of new (i.e., uncached) TLS sessions that a
remote SMTP client is allowed to negotiate with this service per
time unit.
Available in Postfix version 2.9 and later:
smtpd_per_record_deadline (normal: no, overload: yes)
Change the behavior of the smtpd_timeout and smtpd_start-
tls_timeout time limits, from a time limit per read or write
system call, to a time limit to send or receive a complete
record (an SMTP command line, SMTP response line, SMTP message
content line, or TLS protocol message).
Available in Postfix version 3.1 and later:
smtpd_client_auth_rate_limit (0)
The maximal number of AUTH commands that any client is allowed
to send to this service per time unit, regardless of whether or
not Postfix actually accepts those commands.
TARPIT CONTROLS
When a remote SMTP client makes errors, the Postfix SMTP server can
insert delays before responding. This can help to slow down run-away
software. The behavior is controlled by an error counter that counts
the number of errors within an SMTP session that a client makes without
delivering mail.
smtpd_error_sleep_time (1s)
With Postfix version 2.1 and later: the SMTP server response
delay after a client has made more than $smtpd_soft_error_limit
errors, and fewer than $smtpd_hard_error_limit errors, without
delivering mail.
smtpd_soft_error_limit (10)
The number of errors a remote SMTP client is allowed to make
without delivering mail before the Postfix SMTP server slows
down all its responses.
smtpd_hard_error_limit (normal: 20, overload: 1)
The maximal number of errors a remote SMTP client is allowed to
make without delivering mail.
smtpd_junk_command_limit (normal: 100, overload: 1)
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a
remote SMTP client can send before the Postfix SMTP server
starts to increment the error counter with each junk command.
Available in Postfix version 2.1 and later:
smtpd_recipient_overshoot_limit (1000)
The number of recipients that a remote SMTP client can send in
excess of the limit specified with $smtpd_recipient_limit,
before the Postfix SMTP server increments the per-session error
count for each excess recipient.
ACCESS POLICY DELEGATION CONTROLS
As of version 2.1, Postfix can be configured to delegate access policy
decisions to an external server that runs outside Postfix. See the
file SMTPD_POLICY_README for more information.
smtpd_policy_service_max_idle (300s)
The time after which an idle SMTPD policy service connection is
closed.
smtpd_policy_service_max_ttl (1000s)
The time after which an active SMTPD policy service connection
is closed.
smtpd_policy_service_timeout (100s)
The time limit for connecting to, writing to, or receiving from
a delegated SMTPD policy server.
Available in Postfix version 3.0 and later:
smtpd_policy_service_default_action (451 4.3.5 Server configuration
problem)
The default action when an SMTPD policy service request fails.
smtpd_policy_service_request_limit (0)
The maximal number of requests per SMTPD policy service connec-
tion, or zero (no limit).
smtpd_policy_service_try_limit (2)
The maximal number of attempts to send an SMTPD policy service
request before giving up.
smtpd_policy_service_retry_delay (1s)
The delay between attempts to resend a failed SMTPD policy ser-
vice request.
Available in Postfix version 3.1 and later:
smtpd_policy_service_policy_context (empty)
Optional information that the Postfix SMTP server specifies in
the "policy_context" attribute of a policy service request
(originally, to share the same service endpoint among multiple
check_policy_service clients).
ACCESS CONTROLS
The SMTPD_ACCESS_README document gives an introduction to all the SMTP
server access control features.
smtpd_delay_reject (yes)
Wait until the RCPT TO command before evaluating
$smtpd_client_restrictions, $smtpd_helo_restrictions and
$smtpd_sender_restrictions, or wait until the ETRN command
before evaluating $smtpd_client_restrictions and
$smtpd_helo_restrictions.
parent_domain_matches_subdomains (see 'postconf -d' output)
A list of Postfix features where the pattern "example.com" also
matches subdomains of example.com, instead of requiring an
explicit ".example.com" pattern.
smtpd_client_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in
the context of a client connection request.
smtpd_helo_required (no)
Require that a remote SMTP client introduces itself with the
HELO or EHLO command before sending the MAIL command or other
commands that require EHLO negotiation.
smtpd_helo_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in
the context of a client HELO command.
smtpd_sender_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in
the context of a client MAIL FROM command.
smtpd_recipient_restrictions (see 'postconf -d' output)
Optional restrictions that the Postfix SMTP server applies in
the context of a client RCPT TO command, after
smtpd_relay_restrictions.
smtpd_etrn_restrictions (empty)
Optional restrictions that the Postfix SMTP server applies in
the context of a client ETRN command.
allow_untrusted_routing (no)
Forward mail with sender-specified routing
(user[@%!]remote[@%!]site) from untrusted clients to destina-
tions matching $relay_domains.
smtpd_restriction_classes (empty)
User-defined aliases for groups of access restrictions.
smtpd_null_access_lookup_key (<>)
The lookup key to be used in SMTP access(5) tables instead of
the null sender address.
permit_mx_backup_networks (empty)
Restrict the use of the permit_mx_backup SMTP access feature to
only domains whose primary MX hosts match the listed networks.
Available in Postfix version 2.0 and later:
smtpd_data_restrictions (empty)
Optional access restrictions that the Postfix SMTP server
applies in the context of the SMTP DATA command.
smtpd_expansion_filter (see 'postconf -d' output)
What characters are allowed in $name expansions of RBL reply
templates.
Available in Postfix version 2.1 and later:
smtpd_reject_unlisted_sender (no)
Request that the Postfix SMTP server rejects mail from unknown
sender addresses, even when no explicit reject_unlisted_sender
access restriction is specified.
smtpd_reject_unlisted_recipient (yes)
Request that the Postfix SMTP server rejects mail for unknown
recipient addresses, even when no explicit
reject_unlisted_recipient access restriction is specified.
Available in Postfix version 2.2 and later:
smtpd_end_of_data_restrictions (empty)
Optional access restrictions that the Postfix SMTP server
applies in the context of the SMTP END-OF-DATA command.
Available in Postfix version 2.10 and later:
smtpd_relay_restrictions (permit_mynetworks, permit_sasl_authenticated,
defer_unauth_destination)
Access restrictions for mail relay control that the Postfix SMTP
server applies in the context of the RCPT TO command, before
smtpd_recipient_restrictions.
SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS
Postfix version 2.1 introduces sender and recipient address verifica-
tion. This feature is implemented by sending probe email messages that
are not actually delivered. This feature is requested via the
reject_unverified_sender and reject_unverified_recipient access
restrictions. The status of verification probes is maintained by the
verify(8) server. See the file ADDRESS_VERIFICATION_README for infor-
mation about how to configure and operate the Postfix sender/recipient
address verification service.
address_verify_poll_count (normal: 3, overload: 1)
How many times to query the verify(8) service for the completion
of an address verification request in progress.
address_verify_poll_delay (3s)
The delay between queries for the completion of an address veri-
fication request in progress.
address_verify_sender ($double_bounce_sender)
The sender address to use in address verification probes; prior
to Postfix 2.5 the default was "postmaster".
unverified_sender_reject_code (450)
The numerical Postfix SMTP server response code when a recipient
address is rejected by the reject_unverified_sender restriction.
unverified_recipient_reject_code (450)
The numerical Postfix SMTP server response when a recipient
address is rejected by the reject_unverified_recipient restric-
tion.
Available in Postfix version 2.6 and later:
unverified_sender_defer_code (450)
The numerical Postfix SMTP server response code when a sender
address probe fails due to a temporary error condition.
unverified_recipient_defer_code (450)
The numerical Postfix SMTP server response when a recipient
address probe fails due to a temporary error condition.
unverified_sender_reject_reason (empty)
The Postfix SMTP server's reply when rejecting mail with
reject_unverified_sender.
unverified_recipient_reject_reason (empty)
The Postfix SMTP server's reply when rejecting mail with
reject_unverified_recipient.
unverified_sender_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_sender
fails due to a temporary error condition.
unverified_recipient_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_recipi-
ent fails due to a temporary error condition.
Available with Postfix 2.9 and later:
address_verify_sender_ttl (0s)
The time between changes in the time-dependent portion of
address verification probe sender addresses.
ACCESS CONTROL RESPONSES
The following parameters control numerical SMTP reply codes and/or text
responses.
access_map_reject_code (554)
The numerical Postfix SMTP server response code for an access(5)
map "reject" action.
defer_code (450)
The numerical Postfix SMTP server response code when a remote
SMTP client request is rejected by the "defer" restriction.
invalid_hostname_reject_code (501)
The numerical Postfix SMTP server response code when the client
HELO or EHLO command parameter is rejected by the
reject_invalid_helo_hostname restriction.
maps_rbl_reject_code (554)
The numerical Postfix SMTP server response code when a remote
SMTP client request is blocked by the reject_rbl_client,
reject_rhsbl_client, reject_rhsbl_reverse_client,
reject_rhsbl_sender or reject_rhsbl_recipient restriction.
non_fqdn_reject_code (504)
The numerical Postfix SMTP server reply code when a client
request is rejected by the reject_non_fqdn_helo_hostname,
reject_non_fqdn_sender or reject_non_fqdn_recipient restriction.
plaintext_reject_code (450)
The numerical Postfix SMTP server response code when a request
is rejected by the reject_plaintext_session restriction.
reject_code (554)
The numerical Postfix SMTP server response code when a remote
SMTP client request is rejected by the "reject" restriction.
relay_domains_reject_code (554)
The numerical Postfix SMTP server response code when a client
request is rejected by the reject_unauth_destination recipient
restriction.
unknown_address_reject_code (450)
The numerical response code when the Postfix SMTP server rejects
a sender or recipient address because its domain is unknown.
unknown_client_reject_code (450)
The numerical Postfix SMTP server response code when a client
without valid address <=> name mapping is rejected by the
reject_unknown_client_hostname restriction.
unknown_hostname_reject_code (450)
The numerical Postfix SMTP server response code when the host-
name specified with the HELO or EHLO command is rejected by the
reject_unknown_helo_hostname restriction.
Available in Postfix version 2.0 and later:
default_rbl_reply (see 'postconf -d' output)
The default Postfix SMTP server response template for a request
that is rejected by an RBL-based restriction.
multi_recipient_bounce_reject_code (550)
The numerical Postfix SMTP server response code when a remote
SMTP client request is blocked by the reject_multi_recipi-
ent_bounce restriction.
rbl_reply_maps (empty)
Optional lookup tables with RBL response templates.
Available in Postfix version 2.6 and later:
access_map_defer_code (450)
The numerical Postfix SMTP server response code for an access(5)
map "defer" action, including "defer_if_permit" or
"defer_if_reject".
reject_tempfail_action (defer_if_permit)
The Postfix SMTP server's action when a reject-type restriction
fails due to a temporary error condition.
unknown_helo_hostname_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when reject_unknown_helo_host-
name fails due to an temporary error condition.
unknown_address_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when
reject_unknown_sender_domain or reject_unknown_recipient_domain
fail due to a temporary error condition.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf con-
figuration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
command_directory (see 'postconf -d' output)
The location of all postfix administrative commands.
double_bounce_sender (double-bounce)
The sender address of postmaster notifications that are gener-
ated by the mail system.
ipc_timeout (3600s)
The time limit for sending or receiving information over an
internal communication channel.
mail_name (Postfix)
The mail system name that is displayed in Received: headers, in
the SMTP greeting banner, and in bounced mail.
mail_owner (postfix)
The UNIX system account that owns the Postfix queue and most
Postfix daemon processes.
max_idle (100s)
The maximum amount of time that an idle Postfix daemon process
waits for an incoming connection before terminating voluntarily.
max_use (100)
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
myhostname (see 'postconf -d' output)
The internet hostname of this mail system.
mynetworks (see 'postconf -d' output)
The list of "trusted" remote SMTP clients that have more privi-
leges than "strangers".
myorigin ($myhostname)
The domain name that locally-posted mail appears to come from,
and that locally posted mail is delivered to.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
recipient_delimiter (empty)
The set of characters that can separate a user name from its
extension (example: user+foo), or a .forward file name from its
extension (example: .forward+foo).
smtpd_banner ($myhostname ESMTP $mail_name)
The text that follows the 220 status code in the SMTP greeting
banner.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
Available in Postfix version 2.2 and later:
smtpd_forbidden_commands (CONNECT, GET, POST)
List of commands that cause the Postfix SMTP server to immedi-
ately terminate the session with a 221 code.
Available in Postfix version 2.5 and later:
smtpd_client_port_logging (no)
Enable logging of the remote SMTP client port in addition to the
hostname and IP address.
SEE ALSO
anvil(8), connection/rate limiting
cleanup(8), message canonicalization
tlsmgr(8), TLS session and PRNG management
trivial-rewrite(8), address resolver
verify(8), address verification service
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
syslogd(8), system logging
README FILES
ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
ADDRESS_REWRITING_README Postfix address manipulation
FILTER_README, external after-queue content filter
LOCAL_RECIPIENT_README, blocking unknown local recipients
MILTER_README, before-queue mail filter applications
SMTPD_ACCESS_README, built-in access policies
SMTPD_POLICY_README, external policy server
SMTPD_PROXY_README, external before-queue content filter
SASL_README, Postfix SASL howto
TLS_README, Postfix STARTTLS howto
VERP_README, Postfix XVERP extension
XCLIENT_README, Postfix XCLIENT extension
XFORWARD_README, Postfix XFORWARD extension
LICENSE
The Secure Mailer license must be distributed with this software.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
SASL support originally by:
Till Franke
SuSE Rhein/Main AG
65760 Eschborn, Germany
TLS support originally by:
Lutz Jaenicke
BTU Cottbus
Allgemeine Elektrotechnik
Universitaetsplatz 3-4
D-03044 Cottbus, Germany
Revised TLS support by:
Victor Duchovni
Morgan Stanley
SMTPD(8)