It's basically free bash shell script available from: http://wpkg.org/email2fax/index.php/Main_Page

Make sure you have the required tools:

1. libtiff
2. ghostscript
3. mpack/munpack

Where you can e-mail your Asterisk box and it will fax it to the phone number in the subject line.  The good news ends there, it is fairly undocumented and buggy.

Take for example how the documentation mentions you can invoke from the command line like this:

cat "somefile.eml"|email2fax --nodebug

Instead it keeps displaying the help message, I guess this is an oversight but this is supposed to be the stable version.

email2fax
email2fax v1.2beta, email to fax gateway for Asterisk

Usage:

"piped message" | email2fax [OPTIONS]

Options:
--nomail        don't send a confirmation email (default: send confirmation email)
--nodelete      don't delete temporary files (default: delete temporary files)
--nofax         don't send the fax (default: send fax)
--debug         enable debug logging

Email has to contain either one PDF attachment OR one TIFF attachment, and
a destination fax number as a subject.

Examples:

This one sends a fax from the command line, and enables debug logging:

cat message.eml | sudo -u root email2fax --debug


This one enables debug logging, doesn't send a confirmation email,
doesn't delete temporary files, and doesn't send a fax (useful for testing etc.):

cat message.eml | sudo -u root email2fax --debug --nomail --nodelete --nofax


This entry in .procmailrc located in asterisk home directory intercepts all emails
to asterisk, and passes them to email2fax:

:0fw
| /usr/local/bin/email2fax


By default, email2fax logs ALL messages to /var/log/asterisk/faxlog, and saves temporary files in /tmp/email2fax.
These paths, along with several different variables, can be changed
at the beginning of this script (/usr/bin/email2fax).

See http://wpkg.org/email2fax for updates, bug reports, and answers.

I've tried hacking around with the code, it may work if you e-mail and use procmail but judging from the mailing list it sounds like others are having difficulty too.

It's too bad but I thought I'd try this tool, perhaps another day when I have more time.