Hello,
The quota (inbox size) on your account should not result in truncated messages, that problem would result in messages that are too big being bounced back to the original sender. It is more likely that something on your computer is resulting in the images being truncated after downloading them from your e-mail account. Do you have a second e-mail address? I'd be interested to know if the same message it sent to your ATT account, and a copy to a gmail account, if you have a problem downloading the picture attachment from the gmail account. Trying that should help to start narrowing down the source of the problem.
-Raymond