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) dae-
mon, and is placed into the incoming queue as one single
queue file. For this mode of operation, the program
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 con-
nection requests, and for parameters given to HELO, ETRN,
MAIL FROM, VRFY and RCPT TO commands. They are detailed
below and in the main.cf configuration 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 Error 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 4954 (AUTH command)
DIAGNOSTICS
Problems and transactions are logged to syslogd(8).
Depending on the setting of the notify_classes parameter,
the postmaster 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 inter-operability with 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 com-
ments or phrases.
Available in Postfix version 2.1 and later:
resolve_null_domain (no)
Resolve an address that ends in the "@" null domain
as if the local hostname were specified, instead of
rejecting the address as invalid.
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 key-
words (pipelining, starttls, auth, etc.) that the
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 (pipelin-
ing, starttls, auth, etc.) that the 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 ses-
sion id, even when TLS session caching is turned
off (smtpd_tls_session_cache_database is empty).
Available in Postfix version 2.6 and later:
tcp_windowsize (0)
An optional workaround for routers that break TCP
window scaling.
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 filtering, 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 $mydomain; either don't
rewrite message headers from other clients at all,
or rewrite message headers and update incomplete
addresses with the domain specified in the
remote_header_rewrite_domain parameter.
AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 1.0, Postfix can be configured to send new
mail to an external content filter AFTER the mail is
queued. This content filter is expected to inject mail
back into a (Postfix or other) MTA for further delivery.
See the FILTER_README document for details.
content_filter (empty)
The name of a mail delivery transport that filters
mail after it is queued.
BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS
As of version 2.1, the Postfix SMTP server can be config-
ured to send incoming mail to a real-time SMTP-based con-
tent filter BEFORE mail is queued. This content filter is
expected to inject mail back into Postfix. See the
SMTPD_PROXY_README document for details on how to config-
ure and operate this feature.
smtpd_proxy_filter (empty)
The hostname and TCP port of the mail filtering
proxy server.
smtpd_proxy_ehlo ($myhostname)
How the Postfix SMTP server announces itself to the
proxy 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 MILTER_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 pro-
tocol extensions for communication with a Milter
application; prior to Postfix 2.6 the default pro-
tocol is 2.
milter_default_action (tempfail)
The default action when a Milter (mail filter)
application is unavailable or mis-configured.
milter_macro_daemon_name ($myhostname)
The {daemon_name} macro value for Milter (mail fil-
ter) applications.
milter_macro_v ($mail_name $mail_version)
The {v} macro value for Milter (mail filter) appli-
cations.
milter_connect_timeout (30s)
The time limit for connecting to a Milter (mail
filter) application, 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 connec-
tion.
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.
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 filtering, 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 SMTP clients are allowed to use the XFORWARD
feature.
SASL AUTHENTICATION CONTROLS
Postfix SASL support (RFC 4954) can be used to authenti-
cate 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 inter-operability with 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 implementation that is selected
with smtpd_sasl_type.
smtpd_sender_login_maps (empty)
Optional lookup table with the SASL login names
that own 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 Post-
fix 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 configura-
tion files, currently used only to locate the
$smtpd_sasl_path.conf file.
STARTTLS SUPPORT CONTROLS
Detailed information about STARTTLS configuration may be
found in the TLS_README document.
smtpd_tls_security_level (empty)
The SMTP TLS security level for the Postfix SMTP
server; when a non-empty value is specified, this
overrides the obsolete parameters smtpd_use_tls and
smtpd_enforce_tls.
smtpd_sasl_tls_security_options ($smtpd_sasl_secu-
rity_options)
The SASL authentication security options that the
Postfix SMTP server uses for TLS encrypted SMTP
sessions.
smtpd_starttls_timeout (300s)
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 intermediate 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 intermediate CA certifi-
cates.
smtpd_tls_always_issue_session_ids (yes)
Force the Postfix SMTP server to issue a TLS ses-
sion id, even when TLS session caching is turned
off (smtpd_tls_session_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 authentica-
tion over unencrypted connections.
smtpd_tls_ccert_verifydepth (9)
The verification depth for remote SMTP client cer-
tificates.
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 EDH ciphers.
smtpd_tls_dh512_param_file (empty)
File with DH parameters that the Postfix SMTP
server should use with 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 SMTP server cipher list at manda-
tory TLS security levels.
smtpd_tls_mandatory_protocols (SSLv3, TLSv1)
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
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_session_cache_database (empty)
Name of the file containing the optional Postfix
SMTP server TLS session cache.
smtpd_tls_session_cache_timeout (3600s)
The expiration time of Postfix SMTP server TLS ses-
sion cache information.
smtpd_tls_wrappermode (no)
Run the Postfix SMTP server in the non-standard
"wrapper" mode, instead of using the STARTTLS com-
mand.
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
(ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
The OpenSSL cipherlist for "HIGH" grade ciphers.
tls_medium_cipherlist (ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
The OpenSSL cipherlist for "MEDIUM" or higher grade
ciphers.
tls_low_cipherlist (ALL:!EXPORT:+RC4:@STRENGTH)
The OpenSSL cipherlist for "LOW" or higher grade
ciphers.
tls_export_cipherlist (ALL:+RC4:@STRENGTH)
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 used to construct
client-certificate fingerprints for
check_ccert_access and permit_tls_clientcerts.
Available in Postfix version 2.6 and later:
smtpd_tls_protocols (empty)
List of TLS protocols that the Postfix SMTP server
will exclude or include with opportunistic TLS
encryption.
smtpd_tls_ciphers (export)
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 format.
smtpd_tls_eckey_file ($smtpd_tls_eccert_file)
File with the Postfix SMTP server ECDSA private key
in PEM format.
smtpd_tls_eecdh_grade (see 'postconf -d' output)
The Postfix SMTP server security grade for
ephemeral elliptic-curve Diffie-Hellman (EECDH) key
exchange.
tls_eecdh_strong_curve (prime256v1)
The elliptic curve used by the SMTP server for sen-
sibly strong ephemeral ECDH key exchange.
tls_eecdh_ultra_curve (secp384r1)
The elliptic curve used by the SMTP server for max-
imally strong ephemeral ECDH key exchange.
OBSOLETE STARTTLS CONTROLS
The following configuration parameters exist for compati-
bility with Postfix versions before 2.3. Support for these
will be removed in a future release.
smtpd_use_tls (no)
Opportunistic TLS: announce STARTTLS support to
SMTP clients, but do not require that clients use
TLS encryption.
smtpd_enforce_tls (no)
Mandatory TLS: announce STARTTLS support to SMTP
clients, and require that clients use TLS encryp-
tion.
smtpd_tls_cipherlist (empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP
server TLS cipher list.
VERP SUPPORT CONTROLS
With VERP style delivery, each recipient of a message
receives a customized copy of the message with his/her own
recipient address encoded in the envelope sender address.
The VERP_README file describes configuration and operation
details of Postfix support for variable envelope return
path addresses. VERP style delivery is requested with the
SMTP XVERP command or with the "sendmail -V" command-line
option and is available in Postfix version 1.1 and later.
default_verp_delimiters (+=)
The two default VERP delimiter characters.
verp_delimiter_filter (-=+)
The characters Postfix accepts as VERP delimiter
characters on the Postfix sendmail(1) command line
and in SMTP commands.
Available in Postfix version 1.1 and 2.0:
authorized_verp_clients ($mynetworks)
What SMTP clients are allowed to specify the XVERP
command.
Available in Postfix version 2.1 and later:
smtpd_authorized_verp_clients ($authorized_verp_clients)
What SMTP clients are allowed to specify the XVERP
command.
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 pro-
cesses 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 $debug_peer_level.
error_notice_recipient (postmaster)
The recipient of postmaster notifications about
mail delivery problems that are caused by policy,
resource, software or protocol errors.
internal_mail_filter_classes (empty)
What categories of Postfix-generated mail are sub-
ject to before-queue content inspection by
non_smtpd_milters, header_checks and body_checks.
notify_classes (resource, software)
The list of error classes that are reported to the
postmaster.
soft_bounce (no)
Safety net to keep mail queued that would otherwise
be returned to the sender.
Available in Postfix version 2.1 and later:
smtpd_authorized_xclient_hosts (empty)
What SMTP clients are allowed to use the XCLIENT
feature.
KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS
As of Postfix version 2.0, the SMTP server rejects mail
for unknown recipients. This prevents the mail queue from
clogging up with undeliverable MAILER-DAEMON messages.
Additional information on this topic is in the
LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents.
show_user_unknown_table_name (yes)
Display the name of the recipient table in the
"User unknown" responses.
canonical_maps (empty)
Optional address mapping lookup tables for message
headers and envelopes.
recipient_canonical_maps (empty)
Optional address mapping lookup tables for envelope
and header recipient addresses.
Parameters concerning known/unknown local recipients:
mydestination ($myhostname, localhost.$mydomain, local-
host)
The list of domains that are delivered via the
$local_transport mail delivery transport.
inet_interfaces (all)
The network interface addresses that this mail sys-
tem receives mail on.
proxy_interfaces (empty)
The network interface addresses that this mail sys-
tem receives mail on by way of a proxy or network
address translation unit.
inet_protocols (ipv4)
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 $mydestination, $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
$local_recipient_maps specifies a list of lookup
tables that does not match the recipient.
Parameters concerning known/unknown recipients of relay
destinations:
relay_domains ($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 $relay_domains, and
relay_recipient_maps specifies a list of lookup
tables that does not match the recipient address.
Parameters concerning known/unknown recipients in virtual
alias domains:
virtual_alias_domains ($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 SMTP server reply code when a recipient address
matches $virtual_alias_domains, and $vir-
tual_alias_maps specifies a list of lookup tables
that does not match the recipient address.
Parameters concerning known/unknown recipients in virtual
mailbox domains:
virtual_mailbox_domains ($virtual_mailbox_maps)
Postfix is final destination for the specified list
of domains; mail is delivered via the $vir-
tual_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 SMTP server reply code when a recipient address
matches $virtual_mailbox_domains, and $vir-
tual_mailbox_maps specifies a list of lookup tables
that does not match the recipient 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 system 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, stress: 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 lim-
its are implemented in co-operation with the anvil(8) ser-
vice, 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 connection count,
connection rate, or SMTP request rate 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 ses-
sions that a remote SMTP client is allowed to nego-
tiate with this service per time unit.
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 con-
trolled 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, stress: 1)
The maximal number of errors a remote SMTP client
is allowed to make without delivering mail.
smtpd_junk_command_limit (normal: 100, stress: 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.
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_restric-
tions and $smtpd_sender_restrictions, or wait until
the ETRN command before evaluating
$smtpd_client_restrictions and $smtpd_helo_restric-
tions.
parent_domain_matches_subdomains (see 'postconf -d' out-
put)
What Postfix features match subdomains of
"domain.tld" automatically, instead of requiring an
explicit ".domain.tld" pattern.
smtpd_client_restrictions (empty)
Optional SMTP server access restrictions in the
context of a client SMTP connection request.
smtpd_helo_required (no)
Require that a remote SMTP client introduces itself
at the beginning of an SMTP session with the HELO
or EHLO command.
smtpd_helo_restrictions (empty)
Optional restrictions that the Postfix SMTP server
applies in the context of the SMTP HELO command.
smtpd_sender_restrictions (empty)
Optional restrictions that the Postfix SMTP server
applies in the context of the MAIL FROM command.
smtpd_recipient_restrictions (permit_mynetworks,
reject_unauth_destination)
The access restrictions that the Postfix SMTP
server applies in the context of the RCPT TO com-
mand.
smtpd_etrn_restrictions (empty)
Optional SMTP server access restrictions in the
context of a client ETRN request.
allow_untrusted_routing (no)
Forward mail with sender-specified routing
(user[@%!]remote[@%!]site) from untrusted clients
to destinations matching $relay_domains.
smtpd_restriction_classes (empty)
User-defined aliases for groups of access restric-
tions.
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 com-
mand.
smtpd_expansion_filter (see 'postconf -d' output)
What characters are allowed in $name expansions of
RBL reply templates.
Available in Postfix version 2.1 and later:
smtpd_reject_unlisted_sender (no)
Request that the Postfix SMTP server rejects mail
from unknown sender addresses, even when no
explicit reject_unlisted_sender access restriction
is specified.
smtpd_reject_unlisted_recipient (yes)
Request that the Postfix SMTP server rejects mail
for unknown recipient addresses, even when no
explicit reject_unlisted_recipient access restric-
tion is specified.
Available in Postfix version 2.2 and later:
smtpd_end_of_data_restrictions (empty)
Optional access restrictions that the Postfix SMTP
server applies in the context of the SMTP END-OF-
DATA command.
SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS
Postfix version 2.1 introduces sender and recipient
address verification. This feature is implemented by
sending probe email messages that are not actually deliv-
ered. This feature is requested via the reject_unveri-
fied_sender and reject_unverified_recipient access
restrictions. The status of verification probes is main-
tained by the verify(8) server. See the file ADDRESS_VER-
IFICATION_README for information about how to configure
and operate the Postfix sender/recipient address verifica-
tion service.
address_verify_poll_count (3)
How many times to query the verify(8) service for
the completion of an address verification request
in progress.
address_verify_poll_delay (3s)
The delay between queries for the completion of an
address verification request in progress.
address_verify_sender ($double_bounce_sender)
The sender address to use in address verification
probes; prior to Postfix 2.5 the default was "post-
master".
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_unveri-
fied_recipient restriction.
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 tempo-
rary 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 ($reject_temp-
fail_action)
The Postfix SMTP server's action when reject_unver-
ified_sender fails due to a temporary error condi-
tion.
unverified_recipient_tempfail_action ($reject_temp-
fail_action)
The Postfix SMTP server's action when reject_unver-
ified_recipient fails due to a temporary error con-
dition.
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_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_plain-
text_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 Postfix SMTP server response code
when a sender or recipient address is rejected by
the reject_unknown_sender_domain or
reject_unknown_recipient_domain restriction.
unknown_client_reject_code (450)
The numerical Postfix SMTP server response code
when a client without valid address <=> name map-
ping is rejected by the reject_unknown_client_host-
name restriction.
unknown_hostname_reject_code (450)
The numerical Postfix SMTP server response code
when the hostname 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 SMTP server response template for a
request that is rejected by an RBL-based restric-
tion.
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_recipient_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 condi-
tion.
unknown_helo_hostname_tempfail_action ($reject_temp-
fail_action)
The Postfix SMTP server's action when
reject_unknown_helo_hostname fails due to an tempo-
rary error condition.
unknown_address_tempfail_action ($reject_tempfail_action)
The Postfix SMTP server's action when
reject_unknown_sender_domain or
reject_unknown_recipient_domain fail due to a tem-
porary error condition.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and
master.cf configuration 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 com-
mands.
double_bounce_sender (double-bounce)
The sender address of postmaster notifications that
are generated 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 termi-
nating voluntarily.
myhostname (see 'postconf -d' output)
The internet hostname of this mail system.
mynetworks (see 'postconf -d' output)
The list of "trusted" SMTP clients that have more
privileges than "strangers".
myorigin ($myhostname)
The domain name that locally-posted mail appears to
come from, and that locally posted mail is deliv-
ered to.
process_id (read-only)
The process ID of a Postfix command or daemon
process.
process_name (read-only)
The process name of a Postfix command or daemon
process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue direc-
tory.
recipient_delimiter (empty)
The separator between user names and address exten-
sions (user+foo).
smtpd_banner ($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)
The mail system name that is prepended to the
process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
Available in Postfix version 2.2 and later:
smtpd_forbidden_commands (CONNECT, GET, POST)
List of commands that causes the Postfix SMTP
server to immediately 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
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)