NAME
smtpd.conf
—
SMTP daemon configuration
file
DESCRIPTION
smtpd.conf
is the configuration file for
the mail daemon smtpd(8).
When mail arrives, each “RCPT TO:” command generates
a mail envelope. If an envelope matches any of a pre-designated set of
criteria (using the 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 action
directive). If an envelope does not match any options, it is rejected. The
match rules are evaluated sequentially, with the first match winning.
The format of the configuration file is fairly flexible. The
current line can be extended over multiple lines using a backslash
(‘\’). Comments can be put anywhere in the file using a hash
mark (‘#’), 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
listen
, match
, and
port
), must be quoted. Arguments containing
whitespace should be surrounded by double quotes (").
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:
lan_addr = "192.168.0.1" listen on $lan_addr listen on $lan_addr tls auth
The syntax of smtpd.conf
is described
below.
action
name method [options]- When the queue runner processes an envelope from the mail queue, it
carries out the
action
name, selected by thematch
...action
directive when the message was received. Theaction
directive provides configuration data for delivery attempts. Required lookups are performed at the time of each delivery attempt. Consequently, changing anaction
directive or the files it references and restarting the smtpd(8) daemon causes the changes to take effect for subsequent delivery attempts for the respective dispatcher name, even for messages that were already stuck in the queue prior to the configuration changes.The delivery method parameter may be one of the following:
expand-only
- Only accept the message if a delivery method was specified in an aliases or .forward file.
forward-only
- Only accept the message if the recipient results in a remote address after the processing of aliases or forward file.
lmtp
destination [rcpt-to
]- Deliver the message to an LMTP server at
destination. The location may be expressed as
host:port or as a UNIX socket.
Optionally,
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. maildir
[pathname] [junk
]- Deliver the message to the maildir in pathname
if specified, or by default to ~/Maildir.
The pathname may contain format specifiers that are expanded before use (see FORMAT SPECIFIERS).
If the
junk
argument is provided, the message will be moved to the ‘Junk
’ folder if it contains a positive ‘X-Spam
’ header. This folder will be created under pathname if it does not yet exist. mbox
- Deliver the message to the user's mbox with mail.local(8).
mda
command- Delegate the delivery to a command that receives
the message on its standard input.
The command may contain format specifiers that are expanded before use (see FORMAT SPECIFIERS).
relay
- Relay the message to another SMTP server.
The local delivery methods support additional options:
alias
<table>- Use the mapping table for aliases(5) expansion.
ttl
n{s
|m
|h
|d
}- Specify how long a message may remain in the queue.
user
username- Specify the username for performing the
delivery, to be looked up with
getpwnam(3).
This is used for virtual hosting where a single username is in charge of handling delivery for all virtual users.
This option is not usable with the
mbox
delivery method.Only the delivery user's .forward file will be processed.
userbase
<table>- Use the mapping table for user lookups instead
of the
getpwnam(3) function.
The
userbase
does not apply to theuser
option. virtual
<table>- Use the mapping table for virtual expansion. The aliasing table format is described in table(5).
wrapper
name- Use the wrapper specified in
mda wrapper
.
The relay delivery methods also support additional options:
backup
- Operate as a backup mail exchanger delivering messages to any mail exchanger with higher priority.
backup mx
name- Operate as a backup mail exchanger delivering messages to any mail exchanger with higher priority than mail exchanger identified as name.
helo
heloname- Advertise heloname as the hostname to other mail exchangers during the HELO phase.
helo-src
<table>- Use the mapping table to look up a hostname matching the source address, to advertise during the HELO phase.
domain
<domains>- Do not perform MX lookups but look up destination domain in domains and use matching relay url as relay host.
host
relay-url- Do not perform MX lookups but relay messages to the relay host
described by relay-url. The format for
relay-url is
[proto://[label@]]host[:port].
The following protocols are available:
- smtp
- Normal SMTP session with opportunistic STARTTLS (the default).
- smtp+tls
- Normal SMTP session with mandatory STARTTLS.
- smtp+notls
- Plain text SMTP session without TLS.
- lmtp
- LMTP session. port is required.
- smtps
- SMTP session with forced TLS on connection. The default port is 465.
Unless noted, port defaults to 25.
The label corresponds to an entry in a credentials table, as documented in table(5). It is used with the “smtp+tls” and “smtps” protocols for authentication. Server certificates for those protocols are verified by default.
pki
pkiname- For secure connections, use the certificate associated with
pkiname (declared in a
pki
directive) to prove the client's identity to the remote mail server. srs
- When relaying a mail resulting from a forward, use the Sender Rewriting Scheme to rewrite sender address.
tls
[no-verify
]- Require TLS to be used when relaying, using mandatory STARTTLS by
default. When used with a smarthost, the protocol must not be
“smtp+notls://”. If
no-verify
is specified, do not require a valid certificate. protocols
protostr- Define the protocol versions to be used for TLS sessions. Refer to the tls_config_parse_protocols(3) manpage for the format of protostr.
ciphers
cipherstr- Define the list of ciphers that may be used for TLS sessions. Refer to the tls_config_set_ciphers(3) manpage for the format of cipherstr.
auth
<table>- Use the mapping table for connecting to
relay-url using credentials. This option is
usable only with
host
option. The credential table format is described in table(5). mail-from
mailaddr- Use mailaddr as the MAIL FROM address within the SMTP transaction.
src
sourceaddr | <sourceaddr>- Use the string or list table 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.
admd
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.
bounce
warn-interval
delay [, delay ...]- Send warning messages to the envelope sender when temporary delivery
failures cause a message to remain in the queue for longer than
delay. Each delay parameter
consists of a positive decimal integer and a unit
s
,m
,h
, ord
. At most four delay parameters can be specified. The default is "bounce
warn-interval
4h", sending a single warning after four hours. ca
canamecert
cafile- Associate the Certificate Authority (CA) certificate file cafile with ca entry caname. The ca entry can be referenced in listener rules and relay actions.
filter
chain-namechain
{filter-name [, ...]}- Register a chain of filters chain-name, consisting of the filters listed in 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.
filter
filter-namephase
phase-namematch
conditions decision- Register a filter filter-name. A decision about what to do with the mail is taken at phase phase-name when matching conditions. Phases, matching conditions, and decisions are described in MAIL FILTERING, below.
filter
filter-nameproc
proc-name- Register "proc" filter filter-name backed by the proc-name process.
filter
filter-nameproc-exec
command- Register and execute "proc" filter filter-name from command, conformant with the smtpd-filters(7) API. If command starts with a slash it is executed with an absolute path, otherwise it will be run from “/usr/local/libexec/smtpd/”.
include
"pathname"- Replace this directive with the content of the additional configuration file at the absolute pathname.
listen on
interface [family] [options]- Listen on the interface for incoming connections,
using the same syntax as
ifconfig(8). The interface parameter may also
be an interface group, an IP address, or a domain name. Listening can
optionally be restricted to a specific address
family, which can be either
inet4
orinet6
.The options are as follows:
auth
[<authtable>]- 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 authtable, the format of which is described in table(5).
auth-optional
[<authtable>]- Support SMTPAUTH optionally: clients need not authenticate, but may do
so. This allows a
listen on
directive to both accept incoming mail from untrusted senders and permit outgoing mail from authenticated users (usingmatch 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. ca
caname- For secure connections, use the CA certificate associated with
caname (declared in a
ca
directive) as the CA certificate when verifying client certificates. filter
name- Apply filter name on connections handled by this listener.
hostname
hostname- Use hostname in the greeting banner instead of the default server name.
hostnames
<names>- Override the server name for specific addresses. The 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.
mask-src
- Omit the from part when prepending “Received” headers.
no-dsn
- Disable the DSN (Delivery Status Notification) extension.
pki
pkiname- For secure connections, use the certificate associated with
pkiname (declared in a
pki
directive) to prove a mail server's identity. This option can be used multiple times to provide alternate certificates for SNI. port
[port]- Listen on the given port instead of the default port 25.
proxy-v2
- Support the PROXYv2 protocol, appropriately rewriting the source address received from proxy.
received-auth
- In “Received” headers, report whether the session was authenticated and by which local user.
senders
<users> [masquerade
]- Look up the authenticated user in the users
mapping table to find the email addresses that user is allowed to
submit mail as. In addition, if the
masquerade
option is provided, the From header is rewritten to match the sender provided in the SMTP session. smtps
- Support SMTPS, by default on port 465. Mutually exclusive with
tls
. tag
tag- Clients connecting to the listener are tagged with the given tag.
tls
- Support STARTTLS, by default on port 25. Mutually exclusive with
smtps
. tls-require
[verify
]- Like
tls
, but force clients to establish a secure connection before being allowed to start an SMTP transaction. With theverify
option, clients must also provide a valid certificate to establish an SMTP session. protocols
protostr- Define the protocol versions to be used for TLS sessions. Refer to the tls_config_parse_protocols(3) manpage for the format of protostr.
ciphers
cipherstr- Define the list of ciphers that may be used for TLS sessions. Refer to the tls_config_set_ciphers(3) manpage for the format of cipherstr.
listen on
socket
[options]- Listen for incoming SMTP connections on the Unix domain socket
/var/run/smtpd.sock. This is done by default, even
if the directive is absent.
The options are as follows:
filter
name- Apply filter name on connections handled by this listener.
mask-src
- Omit the from part when prepending “Received” headers.
no-dsn
- Disable the DSN (Delivery Status Notification) extension.
tag
tag- Clients connecting to the listener are tagged with the given tag.
match
optionsaction
name- If at least one mail envelope matches the options of
one
match
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 name.The following matching options are supported and can all be negated:
- [
!
]for any
- Specify that session may address any destination.
- [
!
]for local
- Specify that session may address any local domain. This is the default, and may be omitted.
- [
!
]for domain
domain | <domain> - Specify that session may address the string or list table domain.
- [
!
]for domain regex
domain | <domain> - Specify that session may address the regex or regex table domain.
- [
!
]for rcpt-to
recipient | <recipient> - Specify that session may address the string or list table recipient.
- [
!
]for rcpt-to regex
recipient | <recipient> - Specify that session may address the regex or regex table recipient.
- [
!
]from any
- Specify that session may originate from any source.
- [
!
]from auth
- Specify that session may originate from any authenticated user, no matter the source IP address.
- [
!
]from auth
user | <user> - Specify that session may originate from authenticated user or user list user, no matter the source IP address.
- [
!
]from auth regex
user | <user> - Specify that session may originate from authenticated regex or regex list user, no matter the source IP address.
- [
!
]from local
- Specify that session may only originate from a local IP address, or from the local enqueuer. This is the default, and may be omitted.
- [
!
]from mail-from
sender | <sender> - Specify that session may originate from sender or sender list sender, no matter the source IP address.
- [
!
]from mail-from regex
sender | <sender> - Specify that session may originate from regex or regex list sender, no matter the source IP address.
- [
!
]from rdns
- Specify that session may only originate from an IP address that resolves to a reverse DNS.
- [
!
]from rdns
hostname | <hostname> - Specify that session may only originate from an IP address that resolves to a reverse DNS matching string or list string hostname.
- [
!
]from rdns regex
hostname | <hostname> - Specify that session may only originate from an IP address that resolves to a reverse DNS matching regex or list regex hostname.
- [
!
]from socket
- Specify that session may only originate from the local enqueuer.
- [
!
]from src
address | <address> - Specify that session may only originate from string or list table address which can be a specific address or a subnet expressed in CIDR-notation.
- [
!
]from src regex
address | <address> - Specify that session may only originate from regex or regex table address which can be a specific address or a subnet expressed in CIDR-notation.
In addition, the following transaction options may be matched:
- [
!
]auth
- Matches transactions which have been authenticated.
- [
!
]auth
username | <username> - Matches transactions which have been authenticated for user or user list username.
- [
!
]auth regex
username | <username> - Matches transactions which have been authenticated for regex or regex list username.
- [
!
]helo
helo-name | <helo-name> - Specify that session's HELO / EHLO should match the string or list table helo-name.
- [
!
]helo regex
helo-name | <helo-name> - Specify that session's HELO / EHLO should match the regex or regex table helo-name.
- [
!
]mail-from
sender | <sender> - Specify that transaction's MAIL FROM should match the string or list table sender.
- [
!
]mail-from regex
sender | <sender> - Specify that transaction's MAIL FROM should match the regex or regex table sender.
- [
!
]rcpt-to
recipient | <recipient> - Specify that transaction's RCPT TO should match the string or list table recipient.
- [
!
]rcpt-to regex
recipient | <recipient> - Specify that transaction's RCPT TO should match the regex or regex table recipient.
- [
!
]tag
tag - Matches transactions tagged with the given tag.
- [
!
]tag regex
tag - Matches transactions tagged with the given tag regex.
- [
!
]tls
- Specify that transaction should take place in a TLS channel.
- [
match
optionsreject
- Reject the incoming message during the SMTP dialogue. The same
options are supported as for the
match
action
directive. mda
wrapper
name command- Associate command with the mail delivery agent wrapper named name. When a local delivery specifies a wrapper, the command associated with the wrapper will be executed instead. The command may contain format specifiers (see FORMAT SPECIFIERS).
mta
max-deferred
number- When delivery to a given host is suspended due to temporary failures, cache at most number envelopes for that host such that they can be delivered as soon as another delivery succeeds to that host. The default is 100.
pki
pkinamecert
certfile- Associate certificate file certfile with pki entry
pkiname. The pki entry defines a keypair
configuration that can be referenced in listener rules and relay actions.
A certificate chain may be created by appending one or many certificates, including a Certificate Authority certificate, to certfile. The creation of certificates is documented in starttls(8).
pki
pkinamekey
keyfile- Associate the key located in keyfile with pki entry pkiname.
pki
pkinamedhe
params- Specify the DHE parameters to use for DHE cipher suites with pki entry
pkiname. Valid parameter values are
none
,legacy
, andauto
. Forlegacy
, a fixed key length of 1024 bits is used, whereas forauto
, the key length is determined automatically. The default isnone
, which disables DHE cipher suites. proc
proc-name command- Register an external process named proc-name from command, conformant with the smtpd-filters(7) API. Such processes may be used to share the same instance between multiple filters. If command starts with a slash it is executed with an absolute path, otherwise it will be run from “/usr/local/libexec/smtpd/”.
queue
compression
- Store queue files in a compressed format. This may be useful to save disk space.
queue
encryption
[key]- Encrypt queue files with
EVP_aes_256_gcm(3). If no key is
specified, it is read with
getpass(3). If the string
stdin
or a single dash (‘-
’) is given instead of a key, the key is read from the standard input. queue
ttl
delay- Set the default expiration time for temporarily undeliverable messages,
given as a positive decimal integer followed by a unit
s
,m
,h
, ord
. The default is four days (4d). smtp
ciphers
control- Set the control string for SSL_CTX_set_cipher_list(3). The default is "HIGH:!aNULL:!MD5".
smtp limit
max-mails
count- Limit the number of messages to count for each session. The default is 100.
smtp limit
max-rcpt
count- Limit the number of recipients to count for each transaction. The default is 1000.
smtp
max-message-size
size- Reject messages larger than size, given as a positive number of bytes or as a string to be parsed with scan_scaled(3). The default is "35M".
smtp
sub-addr-delim
character- When resolving the local part of a local email address, ignore the ASCII
character and all characters following it. The
default is ‘
+
’. srs
key
secret- Set the secret key to use for SRS, the Sender Rewriting Scheme.
srs
key backup
secret- Set a backup secret key to use as a fallback for SRS. This can be used to implement SRS key rotation.
srs
ttl
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 (4d).
table
name [type:]pathname- Tables provide additional configuration information for
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
table(5) for the exhaustive documentation.
Each table is identified by an arbitrary, unique name.
If the type is
db
, information is stored in a file created with makemap(8); if it isfile
or omitted, information is stored in a plain text file using the format described in table(5). The pathname to the file must be absolute. table
name {value [, ...]}- Instead of using a separate file, declare a list table containing the given static values. The table must contain at least one value and may declare multiple values as a comma-separated (whitespace optional) list.
table
name {key=value [, ...]}- Instead of using a separate file, declare a mapping table containing the given static key-value pairs. The table must contain at least one key-value pair and may declare multiple pairs as a comma-separated (whitespace optional) list.
MAIL FILTERING
In a regular workflow, 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.
Filtering extends the decision making process by allowing 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.
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.
The following phases are currently supported:
connect | upon connection, before a banner is displayed |
helo | after HELO command is submitted |
ehlo | after EHLO command is submitted |
mail-from | after MAIL FROM command is submitted |
rcpt-to | after RCPT TO command is submitted |
data | after DATA command is submitted |
commit | after message is fully is submitted |
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.
fcrdns | forward-confirmed reverse DNS is valid |
rdns | session has a reverse DNS |
rdns <table> | session has a reverse DNS in table |
src <table> | source address is in table |
helo <table> | helo name is in table |
auth | session is authenticated |
auth <table> | session username is in table |
mail-from <table> | sender address is in table |
rcpt-to <table> | recipient address is in table |
These conditions may all be negated by prefixing them with an exclamation mark:
!fcrdns | forward-confirmed reverse DNS is invalid |
Any conditions using a table may indicate that the table contains regular expressions by prefixing the table name with the keyword regex.
helo regex <table> | helo name matches a regex in table |
Finally, a number of decisions may be taken:
bypass | the session or transaction bypasses filters |
disconnect message | the session is disconnected with message |
junk | the session or transaction is junked, i.e., an
‘X-Spam: yes ’ header is added to any
messages |
reject message | the command is rejected with message |
rewrite value | the command parameter is rewritten with value |
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.
FORMAT SPECIFIERS
Some configuration directives support expansion of their
parameters at runtime. Such directives (for example
action
maildir
,
action
mda
) may use format
specifiers which are expanded before delivery or relaying. The following
formats are currently supported:
%{sender} | sender email address, may be empty string |
%{sender.user} | user part of the sender email address, may be empty |
%{sender.domain} | domain part of the sender email address, may be empty |
%{rcpt} | recipient email address |
%{rcpt.user} | user part of the recipient email address |
%{rcpt.domain} | domain part of the recipient email address |
%{dest} | recipient email address after expansion |
%{dest.user} | user part after expansion |
%{dest.domain} | domain part after expansion |
%{user.username} | local user |
%{user.directory} | home directory of the local user |
%{mbox.from} | name used in mbox From separator lines |
%{mda} | mda command, only available for mda wrappers |
Expansion formats also support partial expansion using the optional bracket notations with substring offset. For example, with recipient domain “example.org”:
%{rcpt.domain[0]} | expands to “e” |
%{rcpt.domain[1]} | expands to “x” |
%{rcpt.domain[8:]} | expands to “org” |
%{rcpt.domain[-3:]} | expands to “org” |
%{rcpt.domain[0:6]} | expands to “example” |
%{rcpt.domain[0:-4]} | expands to “example” |
In addition, modifiers may be applied to the token. For example, with recipient “User+Tag@Example.org”:
%{rcpt:lowercase} | expands to “user+tag@example.org” |
%{rcpt:uppercase} | expands to “USER+TAG@EXAMPLE.ORG” |
%{rcpt:strip} | expands to “User@Example.org” |
%{rcpt:lowercase|strip} | expands to “user@example.org” |
For security concerns, expanded values are sanitized and potentially dangerous characters are replaced with ‘:’. In situations where they are desirable, the “raw” modifier may be applied. For example, with recipient “user+t?g@example.org”:
%{rcpt} | expands to “user+t:g@example.org” |
%{rcpt:raw} | expands to “user+t?g@example.org” |
FILES
- /etc/mail/smtpd.conf
- Default smtpd(8) configuration file.
- /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 gethostname(3), either directly if it is a fully qualified domain name, or by retrieving the associated canonical name through getaddrinfo(3).
- /var/run/smtpd.sock
- Unix domain socket for incoming SMTP connections.
- /var/spool/smtpd/
- Spool directories for mail during processing.
EXAMPLES
The default smtpd.conf
file which ships
with OpenBSD listens on the loopback network
interface (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.
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:
# touch /etc/mail/secrets # chmod 640 /etc/mail/secrets # chown root:_smtpd /etc/mail/secrets # echo "bob username:password" > /etc/mail/secrets
smtpd.conf
would look like this:
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 \ auth <secrets> match from local for local action "local_mail" match from local for any action "outbound"
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:
# openssl genrsa -out /etc/ssl/private/mail.example.com.key 4096 # openssl req -new -x509 -key /etc/ssl/private/mail.example.com.key \ -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
In the example above, a certificate valid for one year was created. The configuration file would look like this:
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"
For sites that wish to sign messages using DKIM, the following example uses opensmtpd-filter-dkimsign for DKIM signing:
table aliases file:/etc/mail/aliases filter "dkimsign" proc-exec "filter-dkimsign -d <domain> -s <selector> \ -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"
Alternatively, the
opensmtpd-filter-rspamd
package may be used to provide integration with rspamd, a
third-party daemon which provides multiple antispam features as well as DKIM
signing. As well as configuring rspamd itself, it requires
use of the proc-exec
keyword:
filter "rspamd" proc-exec "filter-rspamd"
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 other-relays to specify the IP addresses of relays that may legitimately originate mail with the owner's domain as the sender.
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 \ reject match from any for domain example.com action "local_mail"
SEE ALSO
mailer.conf(5), table(5), smtpd-filters(7), makemap(8), smtpd(8)
HISTORY
smtpd(8) first appeared in OpenBSD 4.6.