'A' record on my domain name DNS settings being ignored

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http://serverfault.com – Out of the blue over the weekend, something strange has happened to my email server at work, as it suddenly stopped receiving emails. This has nothing to do with the server, but more to the fact that my mail.mydomain.com was being ignored. Ping tests to mail.mydomain.com stopped working, although other.mydomain.com continued to work fine. I've spent three hours on the phone to my ISP (BT) about it, and they couldn't help, except to find that it wasn't their fault. As a workaround, I've used the 'other' A record (within my domain name DNS settings) to do what I need it to do (including adju (HowTos)