Select Security

Select Security Settings

Expand the Screening tree.

Select Hijack Detection

Check Accounts may send no more than X msgs in Y minutes.

X = maximum allowed messages

Y = number of minutes each account can submit X messages

Check Freeze accounts when limit is reached to freeze these accounts.

Select White list to configure accounts that are to be exempt from this feature.

Select Save when finished adding/removing addresses to the White list.

Click Ok

**NOTE - Mailing lists are included in this feature.  If you have mailings lists with more than X memebers, add them to the white list or consider increasing X number of messages.