I've had to move the max size for attachments to 20MB per, and the default user has 100mb for email total. I emphasise the use of personal folders for old emails and zipping files that need to be emailed. If its over 20mb we put it on our FTP site for retreival. I also block all files except Office files, especially .exe, .bat, .vbs, etc, to prevent virus's from getting in through the mail.