Open the Lotus Domino Administrator Client.
Open the Server you want to change
Click on the “Configuration” tab
Twist the Messaging twisty open
Click on Configurations
If you don’t have one for this server you are going to have to create on. I would read up before you do just so that you get it right.
Once you have that open find the “Router/SMTP” tab in the document, then the “Restrictions and Controls” tab.
Click then on the “Restrictions” tab and then you will see two options at the bottom:
Maximum Message Size:
Send all messages as low priority if the message size is between:
I use both of these. You can set the largest mail size in the first box and then set the size you want to filter to be low priority so that it sends out larger files in the off hours of the night and not hog up your bandwidth.