Known issue

To change the alternate delivery host in MailGate 3.1.1, you can use the section with the same name in Administration > Relay > General Settings. When changing only the alternate delivery host in a clustered environment, you might experience mail flow issues in case the alternative delivery host should be used from the secondary box.

Workaround

This is know issue in MailGate 3.1.1, which can easily be solved. After changing the delivery alternative host, go the Administration > Relay > Internal Domains page. Open any of the internal domains and just click Save without changing anything.