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

.\"	$OpenBSD: smtpd.conf.5,v 1.197 2018/06/21 19:33:47 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: June 21 2018 $
.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 actions
(set using the
.Ic action
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 whatever method the action rule specified.
If an envelope does not match any options,
it is rejected.
The
.Ic 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.
.It Cm lmtp Ar destination Op Ar 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,
.Ar 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 Junk
folder if it contains a positive X-Spam header.
.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 for 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 .
.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 host Ar relay-url
Do not perform MX lookups but relay messages to the relay host described by
.Ar relay-url .
If the URL uses TLS, the certificate will be verified by default.
.It Cm tls no-verify
Do not require a valid certificate for the specified host.
.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 address | Pf < Ar address Ns >
Use the string or list table
.Ar address
for the source IP address.
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 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 on 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 host
.Ar caname ,
and use that file as the CA certificate for that host.
.Ar caname
is the server's name,
derived from the default hostname
or set using either
.Pa /etc/mail/mailname
or using the
.Ic hostname
directive.
.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 for
.Xr ifconfig 8 .
The
.Ar interface
parameter may also be an interface group, an IP address, or a domain name.
Listening can optionally be resticted 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 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.
.It Cm port Op Ar port
Listen on the given
.Ar port
instead of the default port 25.
.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.
.El
.It Ic listen on Cm socket Op Cm mask\-src
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.
If the
.Cm mask\-src
option is specified, printing of the HELO name, hostname, and IP
address of the originating host is suppressed in Received: header lines.
.\" XXX The option
.\" Cm filter Ar string
.\" is parsed, but not implemented, see smtpf_session.c.
.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 from any
.Xc
Specify that session may originate from any source.
.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 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.
.El
.Pp
In addition, the following transaction options:
.Bl -tag -width Ds
.It Xo
.Op Ic \&!
.Cm auth
.Xc
Matches transactions which have been authenticated.
.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 mail\-from
.Ar sender | Pf < Ar sender Ns >
.Xc
Specify that transactions's MAIL FROM should match the string or list 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 tag Ar tag
.Xc
Matches transactions tagged with the given
.Ar tag .
.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 host
.Ar pkiname ,
and use that file to prove the identity of the mail server to clients.
.Ar pkiname
is the server's name,
derived from the default hostname
or set using either
.Pa /etc/mail/mailname
or using the
.Ic hostname
directive.
If a fallback certificate or SNI is wanted, the
.Sq *
wildcard may be used as
.Ar pkiname .
.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 host
.Ar pkiname .
.It Ic pki Ar pkiname Cm dhe Ar params
Specify the DHE parameters to use for DHE cipher suites with host
.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 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 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 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 many values as a
list of comma-separated strings.
.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
many pairs as a list of comma-separated
.Ar key Ns = Ns Ar value
descriptions.
.El
.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 the same as 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 "label 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" mbox alias <aliases>
action "relay" relay host tls+auth://label@smtp.example.com \e
	auth <secrets>

match for local action "local"
match for any action "relay"
.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 "relay" relay

match for local action mda_with_aliases
match from any for domain example.com action mda_without_aliases
match for any action "relay"
match auth from any for any action "relay"
.Ed
.Pp
For sites that wish to sign messages using DKIM, the
.Sy dkimproxy
package may be used as a filter.
The following example is the same as the default configuration,
but all outgoing mail is passed to dkimproxy_out on port 10027
for signing.
The signed messages are received on port 10028 and tagged for relaying.
.Bd -literal -offset indent
table aliases file:/etc/mail/aliases

listen on lo0
listen on lo0 port 10028 tag DKIM

action "mbox" mbox alias <aliases>
action "relay" relay
action relay_dkim relay host smtp://127.0.0.1:10027

match for local action "mbox"
match tag DKIM for any action "relay"
match for any action relay_dkim
.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 "mbox" mbox alias <aliases>
action "relay" relay

match for local action "mbox"
match for any action "relay"
match !from src <other-relays> mail\-from "@example.com" for any \e
      reject
match from any for domain example.com action "mbox"
.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 .