Xmail As Testing Smtp Server?, How can I configure XMail as test server

I'd like to use a new instance of XMail as a testing SMTP server that does not actually send outgoing e-mails to anyone. I have an app that sends outgoing e-mails to people and I'd like the app to be able to send outgoing emails to an SMTP server but not have the emails actually go out to anyone. I can look at log files to verify if the proper emails are being sent or look at the email files themselves to verify content.

The TO addresses are from a multitude of domains so I'd like to be able to configure XMail somehow where I don't need to specify individual domains, just configure it so that it never sends anything out. Has anyone done this?

Yes, I realize this forum is sparsely populated but I'm having a hard time googling a solution to this problem. Seems like everyone who has an SMTP server that isn't sending outgoing e-mails wants to "fix" it so it does!

I didn't test it, but it should be very easy. XMail can filter outgoing messages (using filters.out.tab, details are described in manual), so if you set up some "catch all" one:

... then you need just some simple rejecting script/program. As you don't need to do any processing at all, even this should be enough: