I'm new to Watchguard Firewall devices, but I have an XTM 22 running Fireware 11.4 and I am attempting to set it up with an SBS 2008 running behind it using Exchange 2007. I am able to send outgoing mail and browse the internet. I have the SMTP firewall rule setup as I think it should be - however, when I attempt to send a test message externally, I receive a response similar to the following:
Requested action not taken: mailbox unavailable (in reply to MAIL FROM
I have 'googled' this a little, and found references to the SMTP proxy settings causing this.