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

When someone sends an email to captain@deepcurrent.io, their mail server has to figure out where to deliver it. That lookup process is where MX records and A records come in, and they are not interchangeable.

MX records are the right tool for the job. An MX record tells the sending server exactly which mail server handles incoming email for your domain. You can have several, each with a priority level so there's a clear pecking order. If your primary server is down, mail routes to the backup. It's a purpose-built system, and it works reliably.

A record fallback is a last resort, not a strategy. If your domain has no MX record at all, some sending servers will attempt to deliver to the IP address listed in your domain's A record instead. That's the same address your website usually lives on. It was always meant as a safety net for misconfigured domains, not a real mail delivery method.

Here's why leaning on A record fallback causes problems in practice:

• Your web server and your mail server are almost certainly different machines. Pointing mail at your web server IP means it lands somewhere that can't receive it.
• A record fallback has no priority system and no redundancy. There's no backup path if delivery fails.
• Many modern senders don't implement A record fallback at all. If your MX is missing, those senders will simply bounce the message rather than guess.

The practical upshot is simple. Always configure proper MX records. If your MX record is missing or broken, inbound mail will fail, and it'll fail silently for some senders while others send a bounce. Either way, you're losing email.

If you're not sure your MX is set up correctly, you can test your MX resolution in a few minutes. Or if something looks off and you'd rather have a human take a look, our SOS hotline is free.