This web page gives some information on how to adapt your firewall to work with a MH-style mailer (mh, nmh, exmh, ...).
The following information was kindly provided by Ellen Mitchell and Matt Welsh. I don't use MH, so I haven't tried it out myself; I apologize if I get anything wrong here, or mutilate any of Mitchell's or Welsh's suggestions in the translation. Caveat emptor.
The basic problem is that MH tries to contact a SMTP daemon (e.g., sendmail) on localhost to send outgoing email. However, for firewalling, I've suggested to turn off sendmail's SMTP daemon, so this won't work, and all your outgoing email will get lost. So we need to tell MH where to find a SMTP daemon it can use for outgoing email.
Fortunately MH has a configuration file that lets us do this. The configuration file seems to live in /etc/nmh/mts.conf. Once you've found (or created) the config file, add the following two lines:
servers: mnemosyne.cs.berkeley.edu localname: cs.berkeley.eduThis tells MH to use mnemosyne.cs.berkeley.edu's SMTP daemon. (See also the manpage for mh-tailor(5) for more information on the configuration syntax.) Obviously, if you are not in the CS department at UC Berkeley, pick a different mailserver in your own institution.
On older installations, the file is called mtstailor (in a .../lib/mh/ directory; you might have to create the mtstailor file yourself).
In some cases, you may also need to add the following line to the configuration file:
mts: sendmail/smtpbut this may not be necessary on newer installations (I'm not sure).
That should hopefully do it. Feel free to send feedback to me to let me know how it goes. Good luck!