https://superuser.com/questions/883551/smtp-dns-validation-with-multiple-mail-servers-behind-multiple-public-ips I was debating between that and Stack Overflow, and maybe even Network Engineering (my home community), although I couldn't find a definitive answer on whether DNS is considered in scope over there. If there was a better place for this question, where would it be? **Edit:** Thanks for the suggestions guys, I've [re-posted it at Server Fault](https://serverfault.com/questions/673961/smtp-dns-validation-with-multiple-mail-servers-behind-multiple-public-ips). Feel free to delete my post on Super User. Or I guess I can in a few days (once Thor is given a chance to see my response to him).