We are having a problem receiving attachments from one organization when the attachments have a combined total of > 100kb. Our default setting on Exchange is to allow all attachments (non .exe and .vbs) that are < 5mb. Problem comes only from this one organization, as files of similar sizes are allowed when sending from other .org(s), Gmail, or AOL email addresses.
Attachments are generally .pdf, .xls, or .doc. The emails are coming through (not bouncing), however any attachment over the 100kb threshold becomes corrupted. The tech support from that org says that they don't have a problem with any other groups. I have also had that organization send emails to my Gmail account, which also become corrupted. They insist that the attachments themselves are not corrupted, and that they have tested these attachments beforehand.
Our Exchange Server is Win2003 (SP2), Exchange 2003, AVG AV 8.0 Network, and is behind a SonicWall firewall. All of the latest Windows Updates are installed, other than .net framework 3.5.