Q: What is the attachment size limit on MIT's email system?

Answer

Approximately 30 MB.

The answer is approximate. MIT's email system has a maximum message size of 40 MB for both incoming and outgoing messages. This counts everything that goes into a message - your text, plus all the mail headers, plus the all the attachments, needs to fit within the 40 MB limit.

Files expand a little when they are encoded to be attached to email, so the practical limit is a little lower, to give room for the file to grow. 30 MB is a good rule of thumb - a file under 30 MB file will grow when encoded for email, but should still fit within the 40 MB limit for "total message size".

Please note that this is MIT's setting; your recipient's limit may be set much lower, causing your email to bounce back. GMail limit is 25 MB http://mail.google.com/support/bin/answer.py?hl=en&answer=8770