Redundancy is certainly a plus, but you're probably better off handling it on your own, rather than rely on the host.
There are plenty of places that offer backup mail services, like DNSMadeEasy. You can get their service for around $15/year, which gives you an extra 3 records to add.
If your mail server goes down, they'll collect your mail, then forward it back to your primary server when it's back up.
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