This article explains how to disable a user on the SecurityGateway server so that they cannot access their account on the server or send and receive email.
From the Dashboard, after logging in with an administrator account:
Click on Setup/Users in the lower-left corner.
Locate the section labeld Users and Administrators
Under 'Manage Users (select a domain below)' click on the domain that has the user you wish to disable.
Select the user in question and click Edit along the top, or double-click them.
Check the box next to 'This account is disabled'
Click on Save and Exit.
Note that you may also uncheck the box next to their account in the Enabled column.
Additional Comments
Note that disabled users will be unable to send or receive mail, and the SecurityGateway server will give the error 'sender unknown' or 'recipient unknown' when mail is sent from or sent to that address.