Does this make sense ?
Regrettably not in the slightest.
If you think about it logically, both SSL and Unencrypted logins are talking to the same email server.
Thus, if emails are corrupted on the server, they're going to remain so irrespective of how you talk to the server.
My guess is that it is something to do with the way the email is being sent, hence the reason you (or your "IT man what does") will need to take a proper look into the raw email source code, rather than just blankly staring as what the email client decides to parse and render.