mail/extsmail 2.9 OpenBSD

extsmail enables the robust sending of e-mail to external commands. In effect extsmail masquerades as the standard UNIX sendmail program, reading messages, and later trying to send them by user-defined commands. A typical use of extsmail is to allow users who regularly move between different networks and / or find themselves regularly offline, to ensure that their e-mail is sent reliably via ssh to external servers.

In addition to its main purpose, extsmail also allows priority lists to be defined, and also for e-mails to be routed to different servers depending on the e-mail content. The former feature allows one to designate a "preferred" server to send e-mail, but to use a "backup" server if the preferred server is down. The latter feature allows e-mails sent to different e-mail addresses, for example, to be routed to different servers; this allows e-mails to adhere to the IP addressed filtering increasingly used to cut down on spam.