What’s the difference between MX and A record routing?

MX routing: The standard, correct method. Senders look up MX records to find mail servers.

A record fallback: If no MX records exist, RFC 5321 allows trying the domain's A record as the mail server.

Differences:

Flexibility: MX records can point to different servers than your web server. A record fallback uses the same IP.

Priority: MX supports multiple servers with priorities. A record fallback has no redundancy.

Reliability: Many senders do not implement A record fallback. MX is universally supported.

Never rely on A record fallback. Always configure proper MX records.

MX is the official mail delivery address. A record fallback is like sending packages to the general business address and hoping.