Remote system no longer responding

I have problem with remote people sending email with larger attachments (5 to 10 MB) when user sends small email no attachments there is no problem but at the same time same user can send email with larger file attached to email and will get remote system no longer responding message and email is stuck in outgoing mailbox on local, he/she can create another 5-10 messages and those will jump over large one and be send but large one is still outgoing and stuck, it is not related to particular message it is more of a size issue because if user delete this message from outgoing mailbox on local and create different one same issue. It is not configuration size restriction issue, or message priority settings. While I understand that user might have unreliable Internet connection I do not get it why Lotus Notes cannot keep live session while replication large messageAny idea how to solve this issue?