Something was stripping all attachments of all kinds (doc, zip, aif, mp3, txt, cpt, hqx, sea, etc etc etc). I then also started having more problems with NO incoming email. It all started after adding a fourth domain. I removed that domain and all references to it, but the problem persisted. I ended up reinstalling ISPConfig and Postfix, and the problem was still there. I finally just reinstalled the OS, applications, and client data from the backup right before the problem started and everything is fine now. All I can guess is something just flaked out. Thanks for all of your input though! I do appreciate it.
I just hope soon I can help someone else out to repay the help I have received here.