The right way would be something like this

Domain DNS server.

mailserver IN NS mailserver1.domain.com.
mailserver IN NS mailserver2.domain.com.
mailserver IN NS mailserver3.domain.com.

Mailserver1 running dns server

dns entry for mailserver.domain.com

@ IN A machinesip


Mailserver2 running dns server

dns entry for mailserver.domain.com

@ IN A machinesip


Mailserver3 running dns server

dns entry for mailserver.domain.com

@ IN A machinesip