Mail Expiry

How do I change the mail expiry dates, so that emails don’t automatically delete ?

Changes to the Mailbox configuration are made directly to the Mailbox icon, while logged in using the FirstClass application (the Admin app for FirstClass server).

“Right Click” on the Mailbox icon, and get Permissions:
In the resulting dialog, change the Default (which is 48 days), to what ever number works for you, including Never: