Seeing as you just swapped IP's (and you're posted no other DNS dig commands to show the configuration yet) I hate to suggest this because you're not a new forum user, but sometimes it's the simple things - let's take another tact:
Look in your domains list/are your accounts named
user@mail.domain.tld? (simple way to check: run 'zmaccts') If so, 2 options:
A) zmprov -l renameDomain mail.domain.tld domain.tld
(that's a lowercase eLL)
B) Leave that one alone and create domain.com, then simply a lot of:
zmprov renameAccount
user@mail.domain.tld user@domain.tld
(or use the domain drop down list in the admin console gui in the general tab of each account)
After you do either of these you should check for old mentions of mail.domain.com
zmprov gacf | grep mail.domain.com
zmlocalconfig | grep mail.domain.com
etc (for instance the spam/ham accounts might need a pointer fixed, daily email reports address. etc)