I run an email forwarding services so I understand mail system quite well. IMHO, no one seems to use IP in DNS record, probably someone just do quick and dirty

I run an email forwarding services so I understand mail system quite well. IMHO, no one seems to use IP in DNS record, probably someone just do quick and dirty and forgot config. Because when putting IP, when you change your server you have to tell all people to update MX records. So you usually see service use mx1 mx2 style domain. Nowadays, peolple rarel setup mail server and use 3rd solution and they usually alreayd use domain name in their DNS record. So this advice is for people who run their own server who really should know their stuff already.