extsmail.externalsconfigure which external commands to robustly send e-mail via

extsmail.externals is used to configure extsmaild(1). It consists of one or more declarations. Each group consists of zero or more / clauses followed by one or more declarations. An external consists of one or more assignments of pairs.

When sending messages extsmaild(1) first searches through the externals file, in order, for a group whose match / reject clauses match the message in question. If a group does not contain any such clauses it automatically matches all messages. Match / reject clauses currently match only against headers, and use standard POSiX extended regular expressions (see re_format(7) for more details). extsmaild(1) then tries each external in the group, in order, to send the message successfully.

The grammar for this file is as follows:

group    ::= { matches* external+ }

matches  ::= match
           | reject
match    ::= MATCH HEADER string
reject   ::= REJECT HEADER string

external ::= EXTERNAL ID { defn+ }

defn     ::= ID = STRING
           | ID = TIME

TIME     ::= [0-9]+[dhms]

Valid assignments within an external are:

Defines the external shell command used to send e-mail.
If extsmaild(1) is executed in daemon mode, this value defines the length of time that extsmaild(1) will retry this external before giving up and trying the next external in the group. Times are specified as a number followed by (days), (hours), (minutes), or (seconds). If extsmaild(1) is executed in batch mode, the value is ignored.

The configuration file is searched for, in order, in the following locations:

Per-user configuration.

System-wide configuration.

The simplest externals file sending e-mail via ssh(1) looks as follows:

group {
    external mymachine {
        sendmail = "/usr/bin/ssh -q -C -l user mymachine.net /usr/sbin/sendmail -t"
where is a human-friendly name given to an external (it does not effect processing), and is the username on the remote machine .

A more complex example using multiple groups, message matching, and multiple external commands looks as follows:

group {
    match header "^To:.*@foo.com"

    external foo {
        sendmail = "/usr/bin/ssh -q -C -l user shell.foo.com /usr/sbin/sendmail -t"

group {
    external mymachine {
        sendmail = "/usr/bin/ssh -q -C -l user mymachine.net /usr/sbin/sendmail -t"

    external bk {
        sendmail = "/usr/bin/ssh -q -C -l user bk.mymachine.net /usr/sbin/sendmail -t"

extsmail(1), extsmail.conf(5), extsmaild(1)

Laurence Tratt ⟨http://tratt.net/laurie/⟩

November 2, 2008 OpenBSD 7.1