Well, recently I had one of my clients that I host their e-mail system on my web server ask me if they can send more than 2MB for their e-mail attachments.
To do this on a Plesk system, you need to create a new file for the Q-mail.
Plesk defaults to 2MB for e-mail attachments.
Goto this directory:
make a file called “databytes” and store the max number of bytes allowed.
For example, “4000000″ would be max 4MB attachments.