About 12-15 times a day I received emails that are titled " From: Mail Delivery System <mailer-daemon@comcast.net>
Subject: Delivery status notification". It looks like a bounced email from me and the receiver of the the message is always the same: a made up email address "chaplinre@yahoo.com".

Attached to the bounced email in Mail Attachment form is a garbled up email from an actual sender who is trying to email me. The only thing in the attachement is code but I can see who was sending the email so I know if it's one of my clients/friends/etc.

Here is where Zimbra comes in: at the end of each of these mail attachments/garbled emails it says" X-Mailer: Zimbra 6.0.13_GA_2944

So the common denominator between all these messed up emails is that the sender is using Zimbra. So my question is: what can I do? Is this happening because of something set up in my email account? I know it's not a computer problem because it's happening on all of my computers.

I hope you can picture I described above. It's really becoming a huge problem.
Thanks!