I frequently use "mpack" to send attachments from the command line. Unfortunately, when I try to read these messages in SquirrelMail, nothing shows up - not even the attachment or descriptive text showing how to decode the message. At the end of this note is a sample mpacked message that doesn't show up in squirrelmail.
From firstname.lastname@example.org Thu Jan 18 16:52:29 2001
Received: (qmail 25172 invoked by uid 524); 18 Jan 2001 21:52:28 -0000
Date: 18 Jan 2001 21:52:28 -0000
Content-Type: multipart/mixed; boundary="-"
This is a MIME encoded message. Decode it with "munpack" or any other MIME reading software. Mpack/munpack is available via anonymous FTP in ftp.andrew.cmu.edu:pub/mpack/
Content-Type: application/octet-stream; name="error.wav"
Content-Disposition: inline; filename="error.wav"