MTAs don’t care what online analysis tools tell you and setting a null MX for a domain that you don’t receive mail for will work just fine, for the reasons explained in the rfc Having no MX means the smtp connection will fall back to the A record for your domain if one exists --srs ________________________________ From: NANOG <nanog-bounces+ops.lists=gmail.com@nanog.org> on behalf of Pirawat WATANAPONGSE via NANOG <nanog@nanog.org> Sent: Friday, February 26, 2021 3:49:41 PM To: nanog@nanog.org <nanog@nanog.org> Subject: Newbie Question: Is anyone actually using the Null MX (RFC 7505)? Dear all, I put the “Null MX” Record (RFC 7505) into one of my domains yesterday, then those online mail diagnostic tools out there start getting me worried: It looks like most of those tools do not recognize the Null MX as a special case; they just complain that they cannot find the mail server at “.” [Sarcasm: as if the root servers are going to provide mail service to a mere mortal like me!] Among a few shining exceptions (in a good way) is the good ol’ https://bgp.he.net/ which does not show that domain as having any MX record. [maybe it is also wrong, in the other direction?] I fear that the MTAs are going to behave that same way, treating my Null MX as a “misconfigured mail server name” and that my record will mean unnecessary extra queries to the root servers. [well, minus cache hit] So, here comes the questions: 1. Is there anyone actively using this Null MX? If so, may I please see that actual record line (in BIND zone file format) just to satisfy myself that I wrote mine correctly? 2. Which one makes more sense from the practical point-of-view: having a Null MX Record for the no-mail domain, or having no MX record at all? Thanks in advance for all advices, -- Pirawat.