I've got a WPMU dev setup sitting locally and it sent an email out with some password reset information.

Now for reasons I'm not going to go into here that email should simply go out to a JTN domain and come back to me.

It doesn't

Other email sent to that address loops round so all I can assume is that IronPort is just swallowing emails again.

I've no idea if it got eaten going out, or coming back in, but I'm once again in the situation where I know that perfectly valid emails are being eaten and there is apparently nothing I can do about it.

Edited to add: I tested with a non JTN/PN email address (googlemail if you must know) and it all worked fine.