This was a long time in coming...
Squirrelmail, the software which runs UMBC's Webmail email interface was sorely out of date and a recent upgrade (by necessity) of PHP brought to light some stinging incompatibilities between the old Squirrelmail version 1.4.3 and the new version of PHP, so the time was right to put an update in. We're now running Squrrelmail 1.4.6.
Among the problems, the major one users have been complaining about were the corrupted attachment downloads. The attachments on the email servers were always fine, but Squirrelmail parsed them wrong when serving a request from a user to download/view them, and junk always got added to the end of the file. Depending on the file format of the attachement, it was either inconsequential (eg: for images) or it made them unusable (PDF and MS Word documents). This is fixed with tonight's update.