>What is an MTA supposed to do with a message addressed to a domain with >a NULL MX?
Reject it with a 556 status code and 5.1.10 enhanced status code. If the message was already relayed, return a DSN if it makes sense. See section 4.1. You can also feel free to reject mail if the return address has a null MX since you can't reply; in that case it's status 550 and 5.7.27. >I'm looking at some logs and seeing attempts to deliver email to lots of >domains with NULL MX enabled (that have been so for years) and wondering >if I can safely mine these logs and add all the originating MTA IPs to >an internal RBL. That seems reasonable. Any MTA that tries the A address if you publish a null MX (that's "domain MX 0 .") is so broken that it deserves to die if it's not already spamware. There are plenty of MTAs that will sit on the message for a week hoping the next time they look up the MX it will be different, but I can't recall seeing any legitimate MTA for a long time that falls back to A if it finds an MX. The RFC is new but the draft was kicking around since 2006, and was never controversial. R's, John _______________________________________________ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
