MX DNS one IP two domains

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http://serverfault.com – I have two domains: 'example.com' and 'elpmaxe.org' and a server - 'server.example.com' At the moment the mail for 'example.com' is hosted elsewhere so I have set up postfix, dovecot etc to be able to host email on two domains. The setup seems fine with local command line testing. So I have two mx records on 'example.com' pointing to hosted mail servers elsewhere which i want to eventually delete. I have an A record pointing to 123.456.123.456 (server.example.com) on both DNS zones 'example.com' and 'elpmaxe.org' and I did have a 'mail.example.com' MX record pointing to server.example.com i (HowTos)