Here's a good one, when a user creates an appointment on Exchange Server and adds external attendees an email is sent out with the appointment details. Our Exchange Server sends via our Linux SMTP server, it rewrites any firstname.lastname@example.org reply addresses to email@example.com just is case Exchange Server sends mail with that invalid .local FQDN. The external user using Zimbra gets the mail with the correct .co.uk reply address and has the usual option to accept, decline and tentative. When the Zimbra user accepts it looks like Zimbra uses the reply address within the appointment and not the actual email reply address. The address in the appointment is firstname.lastname@example.org so it tries to send and gets rejected. Any thoughts on this one?