If a message sender (the message Return-Path specified with the MAIL FROM protocol command) is a local Object - an Account, or a Group, or a Mailing List in a local Domain, that Domain is opened, and its SMTP Force AUTH option is checked.
If this option is enabled, the message will be rejected if the client mailer has not sent the SMTP AUTH command first. The option value specifies for which sending mailer IP addresses this feature should be used. Note: this option checks for the "fixed" Client IP Addresses only - it does not pay attention to the "temp-client" addresses added with the Process as a Client Address feature.
Note: use this option carefully. Some users may use different mail relays to submit their messages with their CommuniGate Pro Account names as the message Return-Paths. If this option is enabled and those messages are directed to your Server, they will be rejected, because mail relay servers are not able to authenticate the senders on your Server.
Note: most mailers will send the AUTH command only when the server advertises its SMTP AUTH capability. Make sure that your server does advertise it (see above).