SMTPD(8) SMTPD(8)
NAME
smtpd - Postfix SMTP server
SYNOPSIS
smtpd [generic Postfix daemon options]
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 takes an established con-
nection on standard input and deposits messages directly
into the maildrop queue. In this so-called stand-alone
mode, the SMTP server can accept mail even while the mail
system is not running.
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 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2920 (SMTP Pipelining)
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 2554).
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 SMTP clients Postfix will not offer AUTH sup-
port to.
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.
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 rewriting.
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 2554) 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 2554).
smtpd_sasl_auth_enable (no)
Enable SASL authentication in the Postfix SMTP
server.
smtpd_sasl_application_name (smtpd)
The application name used for SASL server initial-
ization.
smtpd_sasl_local_domain (empty)
The name of the local SASL authentication realm.
smtpd_sasl_security_options (noanonymous)
Restrict what authentication mechanisms the Postfix
SMTP server will offer to the client.
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 SMTP clients Postfix will not offer AUTH sup-
port to.
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 $debug_peer_level.
error_notice_recipient (postmaster)
The recipient of postmaster notifications about
mail delivery problems that are caused by policy,
resource, software or protocol errors.
notify_classes (resource, software)
The list of error classes that are reported to the
postmaster.
soft_bounce (no)
Safety net to keep mail queued that would otherwise
be returned to the sender.
Available in Postfix version 2.1 and later:
smtpd_authorized_xclient_hosts (empty)
What SMTP clients are allowed to use the XCLIENT
feature.
KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS
As of Postfix version 2.0, the SMTP server rejects mail
for unknown recipients. This prevents the mail queue from
clogging up with undeliverable MAILER-DAEMON messages.
Additional information on this topic is in the
LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents.
show_user_unknown_table_name (yes)
Display the name of the recipient table in the
"User unknown" responses.
canonical_maps (empty)
Optional address mapping lookup tables for message
headers and envelopes.
recipient_canonical_maps (empty)
Optional address mapping lookup tables for envelope
and header recipient addresses.
Parameters concerning known/unknown local recipients:
mydestination ($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.
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)
Optional list of names 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)
The list of domains that are 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 SMTP server reply code when a recipient address
matches $virtual_mailbox_domains, and $vir-
tual_mailbox_maps specifies a list of lookup tables
that does not match the recipient address.
RESOURCE AND RATE CONTROLS
The following parameters limit resource usage by the SMTP
server and/or control client request rates.
line_length_limit (2048)
Upon input, long lines are chopped up into pieces
of at most this length; upon delivery, long lines
are reconstructed.
queue_minfree (0)
The minimal amount of free space in bytes in the
queue file system that is needed to receive mail.
message_size_limit (10240000)
The maximal size in bytes of a message, including
envelope information.
smtpd_recipient_limit (1000)
The maximal number of recipients that the Postfix
SMTP server accepts per message delivery request.
smtpd_timeout (300s)
The time limit for sending a Postfix SMTP server
response and for receiving a remote SMTP client
request.
smtpd_history_flush_threshold (100)
The maximal number of lines in the Postfix SMTP
server command history before it is flushed upon
receipt of EHLO, RSET, or end of DATA.
Not available in Postfix version 2.1:
smtpd_client_connection_count_limit (50)
How many simultaneous connections any SMTP client
is allowed to make to the SMTP service.
smtpd_client_connection_rate_limit (0)
The maximal number of connection attempts any
client is allowed to make to this service per time
unit.
smtpd_client_connection_limit_exceptions ($mynetworks)
Clients that are excluded from connection count or
connection rate restrictions.
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 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 (20)
The maximal number of errors a remote SMTP client
is allowed to make without delivering mail.
smtpd_junk_command_limit (100)
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.
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 (postmaster)
The sender address to use in address verification
probes.
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.
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
when a client is rejected by an access(5) map
restriction.
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_hostname restric-
tion.
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_hostname, reject_non_fqdn_sender or
reject_non_fqdn_recipient 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
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_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.
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 the next service request
before exiting.
max_use (100)
The maximal number of connection requests before a
Postfix daemon process terminates.
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 pro-
cess.
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 (postfix)
The mail system name that is prepended to the pro-
cess name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
SEE ALSO
cleanup(8), message canonicalization
trivial-rewrite(8), address resolver
verify(8), address verification service
postconf(5), configuration parameters
master(8), process manager
syslogd(8), system logging
README FILES
ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
FILTER_README, external after-queue content filter
LOCAL_RECIPIENT_README, blocking unknown local recipients
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
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
SMTPD(8)