Messaging gateway -Abort message (message timed out)

Hi,

I am having a strange problem only with 1 sender. The sender who works at a bank sends bank stuff every end of month. Every end of month, I get error message Abort message (message timed out); it is only after I have increased the Inbound SMTP Configuration 'Session Timeout' that mail is received. The email is less than 200k. Due to this problem, every end of month I am having to increase the Session Timeout by 5 minutes; today itself I had to set it to 35 minutes.

Where does the problem come from? What can I do to address the problem once for all? Is there like a maximum time for the 'Session Timeout'?

Thanks

Arvind