Backup MX promises email continuity during outages, but without matching your primary server's spam filtering, you've just told spammers where your defenses are weakest.
Most mail servers don't deliver directly to recipients—they hand messages to a smart host that handles the hard parts: reputation, retries, and actually reaching the destination.
Why lower numbers mean higher priority, and how random selection among equals creates load balancing without coordination
Email addresses point to domains, but domains can't receive mail—servers can. MX records tell the Internet which servers speak for your domain.
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