I'm aware that Unsolicited Commercial E-Mail (UCE, a.k.a., spam) has apparently been sent from the MRX.NET domain. It has not.
Mass e-mailers (i.e., spammers) employ a number of tactics to get their documents into you e-mailbox. The simplest trick of all is falsifying the return address (the "From:" on the e-mail) so it appears to come from someplace that it doesn't. That's what's happening here.
One or more spammers are sending e-mail with "mrx.net" in the "From:" part. It's usually some random name like "firstname.lastname@example.org" or "email@example.com."
Even though these e-mails appear to come from MRX.NET, they DO NOT.
Sorry for any inconvenience, but I'll tell you what, it's a problem for me, too. Spammers send e-mail to as many addresses as possible, some even made up. They know that some of the e-mail addresses are non-existent or otherwise unreachable, but they're playing a numbers game: the more they send, the more will actually get through.
Well, guess what happens to all the e-mails that can't be delivered. That's right, they come back to me because they're "From: firstname.lastname@example.org." I'm being literally flooded with returned e-mail.
So it's a problem for all of us. I have some very robust anti-spam technology set up; you should, too. But at the end of the day, the only way to stop spam for good is to remove the economic incentive, so I leave you with this thought...
Don't patronize any company or organization that sends you spam. If we all do this, the spam problem with disappear.