@nospoftombl
Thank you for the log.
I'll fix the crash, but the original cause is a server bug.
The message is "text/plain", but the server returns its mime type as "application/octet-stream".
There is no reason for the app to not trust what it gets from the server, so it treats this message part (the only one) as an attachment.
BODYSTRUCTURE ("application" "octet-stream" NIL NIL NIL "7bit" 255 NIL NIL NIL NIL) INTERNALDATE "28-Mar-2013 20:21:39 +0000")
If you can't get the server company to fix this, I recommend switching to POP3 for this account.