>
> "machines" do not have MX records, domains have MX records.
MX records are associated with the domain but point to machines with
IP addresses running a MTA.
If you don't assign a IP address of a machine with a MTA to the MX
record, then your MX record is useless.
It's essential for fault tolerance to have more than path for your
mailer if you consider your email to be mission critical.
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Enjoy global warming while it lasts.