enables the robust sending of e-mail to external commands

 extsmail masquerades as the standard UNIX sendmail program, reading
 messages, and later piping them to user-defined commands.
 .
 In a sense, extsmail can be thought of as a very simple "tiny" sendmail
 (Think SSMTP, UUCP, ...)
 .
 A typical use is to allow e-mail to be piped via ssh to external servers
 running a full sendmail-compatible MTA. extsmail is designed to have
 sensible defaults, and configuring it is a one-off, quick job.