Nothing Built In. May I suggest that if your architecture can not handle sending messages this large during work hours that you either upgrade your systems, or look for alternative ways to transfer files. ( Yousendit.com, FTP, etc...)

oversize mail will be held in the SMTP queue system. You can create some code that monitor the queue and send mail to senders if mail is oversized. otherwise, why not simply educate your users. lasse at humandata dot se, http://anewmessagehasarrived.blogspot.com

I have scheduled outgoing emails which are greater than 20Mb to be delivered after midnight using the "use differant delivery times for oversize messages" option. this seems to work fine. but I was wondering if it is possible to get exchange to notify the sending user that the message has been delayed \ parked. So far I have not found anything which suggests this is possible. If you know of a way to achieve this, please let me know.

Hi jmv01, Per my knowledge, there isn’t any good way can get Exchange notify the sending user that the message has been delayed\parked. Maybe you can follow Andy and Lasse’s suggestions to help on this issue. Thanks, Evan