path: root/usr.sbin/smtpd/smtpd.conf.5

.\"	$OpenBSD: smtpd.conf.5,v 1.261 2021/08/05 06:33:20 jmc Exp $
.\"
.\" Copyright (c) 2008 Janne Johansson <jj@openbsd.org>
.\" Copyright (c) 2009 Jacek Masiulaniec <jacekm@dobremiasto.net>
.\" Copyright (c) 2012 Gilles Chehade <gilles@poolp.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\"
.Dd $Mdocdate: August 5 2021 $
.Dt SMTPD.CONF 5
.Os
.Sh NAME
.Nm smtpd.conf
.Nd Simple Mail Transfer Protocol daemon configuration file
.Sh DESCRIPTION
.Nm
is the configuration file for the mail daemon
.Xr smtpd 8 .
.Pp
When mail arrives,
each
.Dq RCPT TO:
command generates a mail envelope.
If an envelope matches
any of a pre-designated set of criteria
(using the
.Ic match
directive),
the message is accepted for delivery.
A copy of the message, as well as its associated envelopes,
is saved in the mail queue and later dispatched
according to an associated set of actions
(using the
.Ic action
directive).
If an envelope does not match any options,
it is rejected.
The match rules are evaluated sequentially,
with the first match winning.
.Pp
The format of the configuration file is fairly flexible.
The current line can be extended over multiple lines using a backslash
.Pq Sq \e .
Comments can be put anywhere in the file using a hash mark
.Pq Sq # ,
and extend to the end of the current line.
Care should be taken when commenting out multi-line text:
the comment is effective until the end of the entire block.
Argument names not beginning with a letter, digit, or underscore,
as well as reserved words
(such as
.Ic listen ,
.Ic match ,
and
.Cm port ) ,
must be quoted.
Arguments containing whitespace should be surrounded by double quotes
.Pq \&" .
.Pp
Macros can be defined that are later expanded in context.
Macro names must start with a letter, digit, or underscore,
and may contain any of those characters,
but may not be reserved words.
Macros are not expanded inside quotes.
For example:
.Bd -literal -offset indent
lan_addr = "192.168.0.1"
listen on $lan_addr
listen on $lan_addr tls auth
.Ed
.Pp
The syntax of
.Nm
is described below.
.Bl -tag -width Ds
.It Ic action Ar name method Op Ar options
When the queue runner processes an envelope from the mail queue,
it carries out the
.Ic action
.Ar name ,
selected by the
.Ic match No ... Cm action
directive when the message was received.
The
.Ic action
directive provides configuration data for delivery attempts.
Required lookups are performed at the time of each delivery attempt.
Consequently, changing an
.Ic action
directive or the files it references and restarting the
.Xr smtpd 8
daemon causes the changes to take effect for subsequent delivery
attempts for the respective dispatcher
.Ar name ,
even for messages that were already stuck in the queue
prior to the configuration changes.
.Pp
The delivery
.Ar method
parameter may be one of the following:
.Bl -tag -width Ds
.It Cm expand-only
Only accept the message if a delivery method was specified
in an aliases or
.Pa .forward
file.
.It Cm forward-only
Only accept the message if the recipient results in a remote address
after the processing of aliases or forward file.
.It Cm lmtp Ar destination Op Cm rcpt-to
Deliver the message to an LMTP server at
.Ar destination .
The location may be expressed as host:port or as a UNIX socket.
.Pp
Optionally,
.Cm rcpt-to
might be specified to use the
recipient email address (after expansion) instead of the
local user in the LMTP session as RCPT TO.
.It Cm maildir Op Ar pathname Op Cm junk
Deliver the message to the maildir in
.Ar pathname
if specified, or by default to
.Pa ~/Maildir .
.Pp
The
.Ar pathname
may contain format specifiers that are expanded before use
.Pq see Sx FORMAT SPECIFIERS .
.Pp
If the
.Cm junk
argument is provided, the message will be moved to the
.Ql Junk
folder if it contains a positive
.Ql X-Spam
header.
This folder will be created under
.Ar pathname
if it does not yet exist.
.It Cm mbox
Deliver the message to the user's mbox with
.Xr mail.local 8 .
.It Cm mda Ar command
Delegate the delivery to a
.Ar command
that receives the message on its standard input.
.Pp
The
.Ar command
may contain format specifiers that are expanded before use
.Pq see Sx FORMAT SPECIFIERS .
.It Cm relay
Relay the message to another SMTP server.
.El
.Pp
The local delivery methods support additional options:
.Bl -tag -width Ds
.It Cm alias Pf < Ar table Ns >
Use the mapping
.Ar table
for
.Xr aliases 5
expansion.
.It Xo
.Cm ttl
.Sm off
.Ar n
.Brq Cm s | m | h | d
.Sm on
.Xc
Specify how long a message may remain in the queue.
.It Cm user Ar username
Specify the
.Ar username
for performing the delivery, to be looked up with
.Xr getpwnam 3 .
.Pp
This is used for virtual hosting where a single username
is in charge of handling delivery for all virtual users.
.Pp
This option is not usable with the
.Cm mbox
delivery method.
.It Cm userbase Pf < Ar table Ns >
Use the mapping
.Ar table
for user lookups instead of the
.Xr getpwnam 3
function.
.Pp
The
.Cm userbase
does not apply to the
.Cm user
option.
.It Cm virtual Pf < Ar table Ns >
Use the mapping
.Ar table
for virtual expansion.
The aliasing table format is described in
.Xr table 5 .
.It Cm wrapper Ar name
Use the wrapper specified in
.Cm mda wrapper .
.El
.Pp
The relay delivery methods also support additional options:
.Bl -tag -width Ds
.It Cm backup
Operate as a backup mail exchanger delivering messages to any mail exchanger
with higher priority.
.It Cm backup mx Ar name
Operate as a backup mail exchanger delivering messages to any mail exchanger
with higher priority than mail exchanger identified as
.Ar name .
.It Cm helo Ar heloname
Advertise
.Ar heloname
as the hostname to other mail exchangers during the HELO phase.
.It Cm helo-src Pf < Ar table Ns >
Use the mapping
.Ar table
to look up a hostname matching the source address,
to advertise during the HELO phase.
.It Cm domain Pf < Ar domains Ns >
Do not perform MX lookups but look up destination domain in
.Ar domains
and use matching relay url as relay host.
.It Cm host Ar relay-url
Do not perform MX lookups but relay messages to the relay host described by
.Ar relay-url .
The format for
.Ar relay-url
is
.Sm off
.Op Ar proto No :// Op Ar label No @
.Ar host Op : Ar port .
.Sm on
The following protocols are available:
.Pp
.Bl -tag -width "smtp+notls" -compact
.It smtp
Normal SMTP session with opportunistic STARTTLS
(the default).
.It smtp+tls
Normal SMTP session with mandatory STARTTLS.
.It smtp+notls
Plain text SMTP session without TLS.
.It lmtp
LMTP session.
.Ar port
is required.
.It smtps
SMTP session with forced TLS on connection.
The default port is 465.
.El
.Pp
Unless noted,
.Ar port
defaults to 25.
.Pp
The
.Ar label
corresponds to an entry in a credentials table,
as documented in
.Xr table 5 .
It is used with the
.Dq smtp+tls
and
.Dq smtps
protocols for authentication.
Server certificates for those protocols are verified by default.
.It Cm pki Ar pkiname
For secure connections,
use the certificate associated with
.Ar pkiname
(declared in a
.Ic pki
directive)
to prove the client's identity to the remote mail server.
.It Cm srs
When relaying a mail resulting from a forward,
use the Sender Rewriting Scheme to rewrite sender address.
.It Cm tls Op Cm no-verify
Require TLS to be used when relaying, using mandatory STARTTLS by default.
When used with a smarthost, the protocol must not be
.Dq smtp+notls:// .
If
.Cm no-verify
is specified, do not require a valid certificate.
.It Cm protocols Ar protostr
Define the protocol versions to be used for TLS sessions.
Refer to the
.Xr tls_config_parse_protocols 3
manpage for the format of
.Ar protostr .
.It Cm ciphers Ar cipherstr
Define the list of ciphers that may be used for TLS sessions.
Refer to the
.Xr tls_config_set_ciphers 3
manpage for the format of
.Ar cipherstr .
.It Cm auth Pf < Ar table Ns >
Use the mapping
.Ar table
for connecting to
.Ar relay-url
using credentials.
This option is usable only with
.Cm host
option.
The credential table format is described in
.Xr table 5 .
.It Cm mail-from Ar mailaddr
Use
.Ar mailaddr
as the MAIL FROM address within the SMTP transaction.
.It Cm src Ar sourceaddr | Pf < Ar sourceaddr Ns >
Use the string or list table
.Ar sourceaddr
for the source IP address,
which is useful on machines with multiple interfaces.
If the list contains more than one address, all of them are used
in such a way that traffic is routed as efficiently as possible.
.El
.It Ic admd Ar authservid
The Administrative Management Domain this mail server belongs to.
The authservid will be forwarded to filters using it to identify or mark
authentication-results headers.
If omitted it defaults to the server name.
.It Ic bounce Cm warn-interval Ar delay Op , Ar delay ...
Send warning messages to the envelope sender when temporary delivery
failures cause a message to remain in the queue for longer than
.Ar delay .
Each
.Ar delay
parameter consists of a positive decimal integer and a unit
.Cm s , m , h ,
or
.Cm d .
At most four
.Ar delay
parameters can be specified.
The default is
.Qq Ic bounce Cm warn-interval No 4h ,
sending a single warning after four hours.
.It Ic ca Ar caname Cm cert Ar cafile
Associate the Certificate Authority (CA) certificate file
.Ar cafile
with ca entry
.Ar caname .
The ca entry can be referenced in listener rules and relay actions.
.It Ic filter Ar chain-name Ic chain Brq Ar filter-name Op , Ar ...
Register a chain of filters
.Ar chain-name ,
consisting of the filters listed in
.Ar filter-name .
Filters in a filter chain are executed in order of declaration for
each phase that they are registered for.
A filter chain may be used in place of a filter for any directive except
filter chains themselves.
.It Ic filter Ar filter-name Ic phase Ar phase-name Ic match Ar conditions decision
Register a filter
.Ar filter-name .
A
.Ar decision
about what to do with the mail is taken at phase
.Ar phase-name
when matching
.Ar conditions .
Phases, matching conditions, and decisions are described in
.Sx MAIL FILTERING ,
below.
.It Ic filter Ar filter-name Ic proc Ar proc-name
Register
.Qq proc
filter
.Ar filter-name
backed by the
.Ar proc-name
process.
.It Ic filter Ar filter-name Ic proc-exec Ar command
Register and execute
.Qq proc
filter
.Ar filter-name
from
.Ar command .
If
.Ar command
starts with a slash it is executed with an absolute path,
otherwise it will be run from
.Dq /usr/local/libexec/smtpd/ .
.It Ic include Qq Ar pathname
Replace this directive with the content of the additional configuration
file at the absolute
.Ar pathname .
.It Ic listen on Ar interface Oo Ar family Oc Op Ar options
Listen on the
.Ar interface
for incoming connections, using the same syntax as
.Xr ifconfig 8 .
The
.Ar interface
parameter may also be an interface group, an IP address, or a domain name.
Listening can optionally be restricted to a specific address
.Ar family ,
which can be either
.Cm inet4
or
.Cm inet6 .
.Pp
The
.Ar options
are as follows:
.Bl -tag -width Ds
.It Cm auth Op Pf < Ar authtable Ns >
Support SMTPAUTH: clients may only start SMTP transactions
after successful authentication.
Users are authenticated against either their own normal login credentials
or a credentials table
.Ar authtable ,
the format of which is described in
.Xr table 5 .
.It Cm auth-optional Op Pf < Ar authtable Ns >
Support SMTPAUTH optionally:
clients need not authenticate, but may do so.
This allows a
.Ic listen on
directive to both accept incoming mail from untrusted senders
and permit outgoing mail from authenticated users
(using
.Cm match auth ) .
It can be used in situations
where it is not possible to listen on a separate port
(usually the submission port, 587)
for users to authenticate.
.It Ic ca Ar caname
For secure connections,
use the CA certificate associated with
.Ar caname
(declared in a
.Ic ca
directive)
as the CA certificate when verifying client certificates.
.It Ic filter Ar name
Apply filter
.Ar name
on connections handled by this listener.
.It Cm hostname Ar hostname
Use
.Ar hostname
in the greeting banner instead of the default server name.
.It Cm hostnames Pf < Ar names Ns >
Override the server name for specific addresses.
The
.Ar names
table contains a mapping of IP addresses to hostnames.
If the address on which the connection arrives appears in the mapping,
the associated hostname is used.
.It Cm mask-src
Omit the
.Sy from
part when prepending
.Dq Received
headers.
.It Cm no-dsn
Disable the DSN (Delivery Status Notification) extension.
.It Cm pki Ar pkiname
For secure connections,
use the certificate associated with
.Ar pkiname
(declared in a
.Ic pki
directive)
to prove a mail server's identity.
This option can be used multiple times to provide alternate
certificates for SNI.
.It Cm port Op Ar port
Listen on the given
.Ar port
instead of the default port 25.
.It Cm proxy-v2
Support the PROXYv2 protocol,
appropriately rewriting the source address received from proxy.
.It Cm received-auth
In
.Dq Received
headers, report whether the session was authenticated
and by which local user.
.It Cm senders Pf < Ar users Ns > Op Cm masquerade
Look up the authenticated user in the
.Ar users
mapping table to find the email addresses that user is allowed
to submit mail as.
In addition, if the
.Cm masquerade
option is provided,
the From header is rewritten
to match the sender provided in the SMTP session.
.It Cm smtps
Support SMTPS, by default on port 465.
Mutually exclusive with
.Cm tls .
.It Cm tag Ar tag
Clients connecting to the listener are tagged with the given
.Ar tag .
.It Cm tls
Support STARTTLS, by default on port 25.
Mutually exclusive with
.Cm smtps .
.It Cm tls-require Op Cm verify
Like
.Cm tls ,
but force clients to establish a secure connection
before being allowed to start an SMTP transaction.
With the
.Cm verify
option, clients must also provide a valid certificate
to establish an SMTP session.
.It Cm protocols Ar protostr
Define the protocol versions to be used for TLS sessions.
Refer to the
.Xr tls_config_parse_protocols 3
manpage for the format of
.Ar protostr .
.It Cm ciphers Ar cipherstr
Define the list of ciphers that may be used for TLS sessions.
Refer to the
.Xr tls_config_set_ciphers 3
manpage for the format of
.Ar cipherstr .
.El
.It Ic listen on Cm socket Op Ar options
Listen for incoming SMTP connections on the Unix domain socket
.Pa /var/run/smtpd.sock .
This is done by default, even if the directive is absent.
.Pp
The
.Ar options
are as follows:
.Bl -tag -width Ds
.It Ic filter Ar name
Apply filter
.Ar name
on connections handled by this listener.
.It Cm mask-src
Omit the
.Sy from
part when prepending
.Dq Received
headers.
.It Cm tag Ar tag
Clients connecting to the listener are tagged with the given
.Ar tag .
.El
.It Ic match Ar options Cm action Ar name
If at least one mail envelope matches the
.Ar options
of one
.Ic match Cm action
directive, receive the incoming message, put a copy into each
matching envelope, and atomically save the envelopes to the mail
spool for later processing by the respective dispatcher
.Ar name .
.Pp
The following matching options are supported and can all be negated:
.Bl -tag -width Ds
.It Xo
.Op Ic \&!
.Cm for any
.Xc
Specify that session may address any destination.
.It Xo
.Op Ic \&!
.Cm for local
.Xc
Specify that session may address any local domain.
This is the default, and may be omitted.
.It Xo
.Op Ic \&!
.Cm for domain
.Ar domain | Pf < Ar domain Ns >
.Xc
Specify that session may address the string or list table
.Ar domain .
.It Xo
.Op Ic \&!
.Cm for domain regex
.Ar domain | Pf < Ar domain Ns >
.Xc
Specify that session may address the regex or regex table
.Ar domain .
.It Xo
.Op Ic \&!
.Cm for rcpt-to
.Ar recipient | Pf < Ar recipient Ns >
.Xc
Specify that session may address the string or list table
.Ar recipient .
.It Xo
.Op Ic \&!
.Cm for rcpt-to regex
.Ar recipient | Pf < Ar recipient Ns >
.Xc
Specify that session may address the regex or regex table
.Ar recipient .
.It Xo
.Op Ic \&!
.Cm from any
.Xc
Specify that session may originate from any source.
.It Xo
.Op Ic \&!
.Cm from auth
.Xc
Specify that session may originate from any authenticated user,
no matter the source IP address.
.It Xo
.Op Ic \&!
.Cm from auth
.Ar user | Pf < Ar user Ns >
.Xc
Specify that session may originate from authenticated user or user list
.Ar user ,
no matter the source IP address.
.It Xo
.Op Ic \&!
.Cm from auth regex
.Ar user | Pf < Ar user Ns >
.Xc
Specify that session may originate from authenticated regex or regex list
.Ar user ,
no matter the source IP address.
.It Xo
.Op Ic \&!
.Cm from local
.Xc
Specify that session may only originate from a local IP address,
or from the local enqueuer.
This is the default, and may be omitted.
.It Xo
.Op Ic \&!
.Cm from mail-from
.Ar sender | Pf < Ar sender Ns >
.Xc
Specify that session may originate from sender or sender list
.Ar sender ,
no matter the source IP address.
.It Xo
.Op Ic \&!
.Cm from mail-from regex
.Ar sender | Pf < Ar sender Ns >
.Xc
Specify that session may originate from regex or regex list
.Ar sender ,
no matter the source IP address.
.It Xo
.Op Ic \&!
.Cm from rdns
.Xc
Specify that session may only originate from an IP address that
resolves to a reverse DNS.
.It Xo
.Op Ic \&!
.Cm from rdns
.Ar hostname | Pf < Ar hostname Ns >
.Xc
Specify that session may only originate from an IP address that
resolves to a reverse DNS matching string or list string
.Ar hostname .
.It Xo
.Op Ic \&!
.Cm from rdns regex
.Ar hostname | Pf < Ar hostname Ns >
.Xc
Specify that session may only originate from an IP address that
resolves to a reverse DNS matching regex or list regex
.Ar hostname .
.It Xo
.Op Ic \&!
.Cm from socket
.Xc
Specify that session may only originate from the local enqueuer.
.It Xo
.Op Ic \&!
.Cm from src
.Ar address | Pf < Ar address Ns >
.Xc
Specify that session may only originate from string or list table
.Ar address
which can be a specific address or a subnet expressed in CIDR-notation.
.It Xo
.Op Ic \&!
.Cm from src regex
.Ar address | Pf < Ar address Ns >
.Xc
Specify that session may only originate from regex or regex table
.Ar address
which can be a specific address or a subnet expressed in CIDR-notation.
.El
.Pp
In addition, the following transaction options may be matched:
.Bl -tag -width Ds
.It Xo
.Op Ic \&!
.Cm auth
.Xc
Matches transactions which have been authenticated.
.It Xo
.Op Ic \&!
.Cm auth
.Ar username | Pf < Ar username Ns >
.Xc
Matches transactions which have been authenticated for user or user list
.Ar username .
.It Xo
.Op Ic \&!
.Cm auth regex
.Ar username | Pf < Ar username Ns >
.Xc
Matches transactions which have been authenticated for regex or regex list
.Ar username .
.It Xo
.Op Ic \&!
.Cm helo
.Ar helo-name | Pf < Ar helo-name Ns >
.Xc
Specify that session's HELO / EHLO should match the string or list table
.Ar helo-name .
.It Xo
.Op Ic \&!
.Cm helo regex
.Ar helo-name | Pf < Ar helo-name Ns >
.Xc
Specify that session's HELO / EHLO should match the regex or regex table
.Ar helo-name .
.It Xo
.Op Ic \&!
.Cm mail-from
.Ar sender | Pf < Ar sender Ns >
.Xc
Specify that transaction's MAIL FROM should match the string or list table
.Ar sender .
.It Xo
.Op Ic \&!
.Cm mail-from regex
.Ar sender | Pf < Ar sender Ns >
.Xc
Specify that transaction's MAIL FROM should match the regex or regex table
.Ar sender .
.It Xo
.Op Ic \&!
.Cm rcpt-to
.Ar recipient | Pf < Ar recipient Ns >
.Xc
Specify that transaction's RCPT TO should match the string or list table
.Ar recipient .
.It Xo
.Op Ic \&!
.Cm rcpt-to regex
.Ar recipient | Pf < Ar recipient Ns >
.Xc
Specify that transaction's RCPT TO should match the regex or regex table
.Ar recipient .
.It Xo
.Op Ic \&!
.Cm tag Ar tag
.Xc
Matches transactions tagged with the given
.Ar tag .
.It Xo
.Op Ic \&!
.Cm tag regex Ar tag
.Xc
Matches transactions tagged with the given
.Ar tag
regex.
.It Xo
.Op Ic \&!
.Cm tls
.Xc
Specify that transaction should take place in a TLS channel.
.El
.It Ic match Ar options Cm reject
Reject the incoming message during the SMTP dialogue.
The same
.Ar options
are supported as for the
.Ic match Cm action
directive.
.It Ic mda Cm wrapper Ar name command
Associate
.Ar command
with the mail delivery agent wrapper named
.Ar name .
When a local delivery specifies a wrapper, the
.Ar command
associated with the wrapper will be executed instead.
The command may contain format specifiers
.Pq see Sx FORMAT SPECIFIERS .
.It Ic mta Cm max-deferred Ar number
When delivery to a given host is suspended due to temporary failures,
cache at most
.Ar number
envelopes for that host such that they can be delivered
as soon as another delivery succeeds to that host.
The default is 100.
.It Ic pki Ar pkiname Cm cert Ar certfile
Associate certificate file
.Ar certfile
with pki entry
.Ar pkiname .
The pki entry defines a keypair configuration that can be referenced
in listener rules and relay actions.
.Pp
A certificate chain may be created by appending one or many certificates,
including a Certificate Authority certificate,
to
.Ar certfile .
The creation of certificates is documented in
.Xr starttls 8 .
.It Ic pki Ar pkiname Cm key Ar keyfile
Associate the key located in
.Ar keyfile
with pki entry
.Ar pkiname .
.It Ic pki Ar pkiname Cm dhe Ar params
Specify the DHE parameters to use for DHE cipher suites with pki entry
.Ar pkiname .
Valid parameter values are
.Cm none ,
.Cm legacy ,
and
.Cm auto .
For
.Cm legacy ,
a fixed key length of 1024 bits is used, whereas for
.Cm auto ,
the key length is determined automatically.
The default is
.Cm none ,
which disables DHE cipher suites.
.It Ic proc Ar proc-name Ar command
Register an external process named
.Ar proc-name
from
.Ar command .
Such processes may be used to share the same instance between multiple filters.
If
.Ar command
starts with a slash it is executed with an absolute path,
otherwise it will be run from
.Dq /usr/local/libexec/smtpd/ .
.It Ic queue Cm compression
Store queue files in a compressed format.
This may be useful to save disk space.
.It Ic queue Cm encryption Op Ar key
Encrypt queue files with
.Xr EVP_aes_256_gcm 3 .
If no
.Ar key
is specified, it is read with
.Xr getpass 3 .
If the string
.Cm stdin
or a single dash
.Pq Ql -
is given instead of a
.Ar key ,
the key is read from the standard input.
.It Ic queue Cm ttl Ar delay
Set the default expiration time for temporarily undeliverable
messages, given as a positive decimal integer followed by a unit
.Cm s , m , h ,
or
.Cm d .
The default is four days
.Pq 4d .
.It Ic smtp Cm ciphers Ar control
Set the
.Ar control
string for
.Xr SSL_CTX_set_cipher_list 3 .
The default is
.Qq HIGH:!aNULL:!MD5 .
.It Ic smtp limit Cm max-mails Ar count
Limit the number of messages to
.Ar count
for each session.
The default is 100.
.It Ic smtp limit Cm max-rcpt Ar count
Limit the number of recipients to
.Ar count
for each transaction.
The default is 1000.
.It Ic smtp Cm max-message-size Ar size
Reject messages larger than
.Ar size ,
given as a positive number of bytes or as a string to be parsed with
.Xr scan_scaled 3 .
The default is
.Qq 35M .
.It Ic smtp Cm sub-addr-delim Ar character
When resolving the local part of a local email address, ignore the ASCII
.Ar character
and all characters following it.
The default is
.Ql + .
.It Ic srs Cm key Ar secret
Set the secret key to use for SRS,
the Sender Rewriting Scheme.
.It Ic srs Cm key backup Ar secret
Set a backup secret key to use as a fallback for SRS.
This can be used to implement SRS key rotation.
.It Ic srs Cm ttl Ar delay
Set the time-to-live delay for SRS envelopes.
After this delay,
a bounce reply to the SRS address will be discarded
to limit risks of forged addresses.
The default is four days
.Pq 4d .
.It Ic table Ar name Oo Ar type : Oc Ns Ar pathname
Tables provide additional configuration information for
.Xr smtpd 8
in the form of lists or key-value mappings.
The format of the entries depends on what the table is used for.
Refer to
.Xr table 5
for the exhaustive documentation.
.Pp
Each table is identified by an arbitrary, unique
.Ar name .
.Pp
If the
.Ar type
is
.Cm db ,
information is stored in a file created with
.Xr makemap 8 ;
if it is
.Cm file
or omitted, information is stored in a plain text file
using the format described in
.Xr table 5 .
The
.Ar pathname
to the file must be absolute.
.It Ic table Ar name Brq Ar value Op , Ar ...
Instead of using a separate file, declare a list table
containing the given static
.Ar value Ns s .
The table must contain at least one value and may declare multiple values as a
comma-separated (whitespace optional) list.
.It Ic table Ar name Brq Ar key Ns = Ns Ar value Op , Ar ...
Instead of using a separate file, declare a mapping table
containing the given static
.Ar key Ns - Ns Ar value
pairs.
The table must contain at least one key-value pair and may declare
multiple pairs as a comma-separated (whitespace optional) list.
.El
.Ss MAIL FILTERING
In a regular workflow,
.Xr smtpd 8
may accept or reject a message based only on the content of envelopes.
Its decisions are about the handling of the message,
not about the handling of an active session.
.Pp
Filtering extends the decision making process by allowing
.Xr smtpd 8
to stop at each phase of an SMTP session,
check that conditions are met,
then decide if a session is allowed to move forward.
.Pp
With filtering,
a session may be interrupted at any phase before an envelope is complete.
A message may also be rejected after being submitted,
regardless of whether the envelope was accepted or not.
.Pp
The following phases are currently supported:
.Bl -column mail-from -offset indent
.It connect    Ta upon connection, before a banner is displayed
.It helo       Ta after HELO command is submitted
.It ehlo       Ta after EHLO command is submitted
.It mail-from Ta after MAIL FROM command is submitted
.It rcpt-to   Ta after RCPT TO command is submitted
.It data       Ta after DATA command is submitted
.It commit     Ta after message is fully is submitted
.El
.Pp
At each phase, various conditions may be matched.
The fcrdns, rdns, and src data are available in all phases,
but other data must have been already submitted before they are available.
.Bl -column XXXXXXXXXXXXXXXXXXXXX -offset indent
.It fcrdns                        Ta forward-confirmed reverse DNS is valid
.It rdns                          Ta session has a reverse DNS
.It rdns Pf < Ar table Ns >       Ta session has a reverse DNS in table
.It src Pf < Ar table Ns >        Ta source address is in table
.It helo Pf < Ar table Ns >       Ta helo name is in table
.It auth                          Ta session is authenticated
.It auth Pf < Ar table Ns >       Ta session username is in table
.It mail-from Pf < Ar table Ns >  Ta sender address is in table
.It rcpt-to Pf < Ar table Ns >    Ta recipient address is in table
.El
.Pp
These conditions may all be negated by prefixing them with an exclamation mark:
.Bl -column XXXXXXXXXXXXXXXXXXXXX -offset indent
.It !fcrdns                     Ta forward-confirmed reverse DNS is invalid
.El
.Pp
Any conditions using a table may indicate that the table contains regular
expressions by prefixing the table name with the keyword regex.
.Bl -column XXXXXXXXXXXXXXXXXXXXX -offset indent
.It helo regex Pf < Ar table Ns >       Ta helo name matches a regex in table
.El
.Pp
Finally, a number of decisions may be taken:
.Bl -column XXXXXXXXXXXXXXXXXXXXX -offset indent
.It bypass                Ta the session or transaction bypasses filters
.It disconnect Ar message Ta the session is disconnected with message
.It junk                  Ta the session or transaction is junked, i.e., an
.Ql X-Spam: yes
header is added to any messages
.It reject Ar message     Ta the command is rejected with message
.It rewrite Ar value      Ta the command parameter is rewritten with value
.El
.Pp
Decisions that involve a message require that the message be RFC valid,
meaning that they should either start with a 4xx or 5xx status code.
Decisions can be taken at any phase,
though junking can only happen before a message is committed.
.Ss FORMAT SPECIFIERS
Some configuration directives support expansion of their parameters at runtime.
Such directives (for example
.Ic action Cm maildir ,
.Ic action Cm mda )
may use format specifiers which are expanded before delivery or
relaying.
The following formats are currently supported:
.Bl -column %{user.directory} -offset indent
.It %{sender}         Ta sender email address, may be empty string
.It %{sender.user}    Ta user part of the sender email address, may be empty
.It %{sender.domain}  Ta domain part of the sender email address, may be empty
.It %{rcpt}           Ta recipient email address
.It %{rcpt.user}      Ta user part of the recipient email address
.It %{rcpt.domain}    Ta domain part of the recipient email address
.It %{dest}           Ta recipient email address after expansion
.It %{dest.user}      Ta user part after expansion
.It %{dest.domain}    Ta domain part after expansion
.It %{user.username}  Ta local user
.It %{user.directory} Ta home directory of the local user
.It %{mbox.from}      Ta name used in mbox From separator lines
.It %{mda}            Ta mda command, only available for mda wrappers
.El
.Pp
Expansion formats also support partial expansion using the optional
bracket notations with substring offset.
For example, with recipient domain
.Dq example.org :
.Bl -column %{rcpt.domain[0:-4]} -offset indent
.It %{rcpt.domain[0]}    Ta expands to Dq e
.It %{rcpt.domain[1]}    Ta expands to Dq x
.It %{rcpt.domain[8:]}   Ta expands to Dq org
.It %{rcpt.domain[-3:]} Ta expands to Dq org
.It %{rcpt.domain[0:6]}  Ta expands to Dq example
.It %{rcpt.domain[0:-4]} Ta expands to Dq example
.El
.Pp
In addition, modifiers may be applied to the token.
For example, with recipient
.Dq User+Tag@Example.org :
.Bl -column %{rcpt:lowercase|strip} -offset indent
.It %{rcpt:lowercase}       Ta expands to Dq user+tag@example.org
.It %{rcpt:uppercase}       Ta expands to Dq USER+TAG@EXAMPLE.ORG
.It %{rcpt:strip}           Ta expands to Dq User@Example.org
.It %{rcpt:lowercase|strip} Ta expands to Dq user@example.org
.El
.Pp
For security concerns, expanded values are sanitized and potentially
dangerous characters are replaced with
.Sq \&: .
In situations where they are desirable, the
.Dq raw
modifier may be applied.
For example, with recipient
.Dq user+t?g@example.org :
.Bl -column %{rcpt:raw} -offset indent
.It %{rcpt}     Ta expands to Dq user+t:g@example.org
.It %{rcpt:raw} Ta expands to Dq user+t?g@example.org
.El
.Sh FILES
.Bl -tag -width "/etc/mail/smtpd.confXXX" -compact
.It Pa /etc/mail/smtpd.conf
Default
.Xr smtpd 8
configuration file.
.It Pa /etc/mail/mailname
If this file exists,
the first line is used as the server name.
Otherwise, the server name is derived from the local hostname returned by
.Xr gethostname 3 ,
either directly if it is a fully qualified domain name,
or by retrieving the associated canonical name through
.Xr getaddrinfo 3 .
.It Pa /var/run/smtpd.sock
Unix domain socket for incoming SMTP connections.
.It Pa /var/spool/smtpd/
Spool directories for mail during processing.
.El
.Sh EXAMPLES
The default
.Nm
file which ships with
.Ox
listens on the loopback network interface
.Pq Pa lo0
and allows for mail from users and daemons on the local machine,
as well as permitting email to remote servers.
Some more complex configurations are given below.
.Pp
This first example is similar to the default configuration,
but all outgoing mail is forwarded to a remote SMTP server.
A secrets file is needed to specify a username and password:
.Bd -literal -offset indent
# touch /etc/mail/secrets
# chmod 640 /etc/mail/secrets
# chown root:_smtpd /etc/mail/secrets
# echo "bob username:password" > /etc/mail/secrets
.Ed
.Pp
.Nm
would look like this:
.Bd -literal -offset indent
table aliases file:/etc/mail/aliases
table secrets file:/etc/mail/secrets

listen on lo0

action "local_mail" mbox alias <aliases>
action "outbound" relay host smtp+tls://bob@smtp.example.com \e
	auth <secrets>

match from local for local action "local_mail"
match from local for any action "outbound"
.Ed
.Pp
In this second example,
the aim is to permit mail delivery and relaying
only for users that can authenticate
(using their normal login credentials).
An RSA certificate must be provided to prove the server's identity.
The mail server listens on all interfaces the default routes point to.
Mail with a local destination is sent to an external MDA.
First, the RSA certificate is created:
.Bd -literal -offset indent
# openssl genrsa \-out /etc/ssl/private/mail.example.com.key 4096
# openssl req \-new \-x509 \-key /etc/ssl/private/mail.example.com.key \e
	\-out /etc/ssl/mail.example.com.crt \-days 365
# chmod 600 /etc/ssl/mail.example.com.crt
# chmod 600 /etc/ssl/private/mail.example.com.key
.Ed
.Pp
In the example above,
a certificate valid for one year was created.
The configuration file would look like this:
.Bd -literal -offset indent
pki mail.example.com cert "/etc/ssl/mail.example.com.crt"
pki mail.example.com key "/etc/ssl/private/mail.example.com.key"

table aliases file:/etc/mail/aliases

listen on lo0
listen on egress tls pki mail.example.com auth

action mda_with_aliases mda "/path/to/mda \-f \-" alias <aliases>
action mda_without_aliases mda "/path/to/mda \-f \-"
action "outbound" relay

match for local action mda_with_aliases
match from any for domain example.com action mda_without_aliases
match for any action "outbound"
match auth from any for any action "outbound"
.Ed
.Pp
For sites that wish to sign messages using DKIM,
the following example uses
.Sy opensmtpd-filter-dkimsign
for DKIM signing:
.Bd -literal -offset indent
table aliases file:/etc/mail/aliases

filter "dkimsign" proc-exec "filter-dkimsign -d <domain> -s <selector> \e
	-k /etc/mail/dkim/private.key" user _dkimsign group _dkimsign

listen on socket filter "dkimsign"
listen on lo0 filter "dkimsign"

action "local_mail" mbox alias <aliases>
action "outbound" relay

match for local action "local_mail"
match for any action "outbound"
.Ed
.Pp
Alternatively, the
.Sy opensmtpd-filter-rspamd
package may be used to provide integration with
.Sy rspamd ,
a third-party daemon which provides multiple antispam features
as well as DKIM signing.
As well as configuring
.Sy rspamd
itself,
it requires use of the
.Cm proc-exec
keyword:
.Bd -literal -offset indent
filter "rspamd" proc-exec "filter-rspamd"
.Ed
.Pp
Sites that accept non-local messages may be able to cut down on the
volume of spam received by rejecting forged messages that claim
to be from the local domain.
The following example uses a list table
.Em other-relays
to specify the IP addresses of relays that may legitimately
originate mail with the owner's domain as the sender.
.Bd -literal -offset indent
table aliases file:/etc/mail/aliases
table other-relays file:/etc/mail/other-relays

listen on lo0
listen on egress

action "local_mail" mbox alias <aliases>
action "outbound" relay

match for local action "local_mail"
match for any action "outbound"
match !from src <other-relays> mail\-from "@example.com" for any \e
      reject
match from any for domain example.com action "local_mail"
.Ed
.Sh SEE ALSO
.Xr mailer.conf 5 ,
.Xr table 5 ,
.Xr makemap 8 ,
.Xr smtpd 8
.Sh HISTORY
.Xr smtpd 8
first appeared in
.Ox 4.6 .