Interesting case.
I have a server which has been up for several years. Just recently, my own email account stopped being able to send emails with attachments.
This is what happens. From either my computer at home or at work, I send a message to myself through my AMS and the message disappears after the mail transaction is closed.
I can change the mail settings on my computer to my wife's IMAP/SMTP account and then send the same message and the message arrives with no problem.
Using my own account IMAP/SMTP settings, the sent message appears in my sent box as if sent, and the server logs say the transaction completed, but the mail disappears and never makes it to the recipient.
The only different is whether it is beng sent using my account setting sor my wifes account settings (both accounts are on my AMS server).
Any ideas? Should I delete my account on the server and recreate it?