An MX (Mail Exchanger) record tells the internet which mail server(s) handle email for a domain. A domain can have multiple MX records, each with a priority (also called "preference") value — and that number determines the order in which sending mail servers try to deliver a message.
This trips up a lot of people: a lower priority number means higher priority. An MX record with priority 10 is tried before one with priority 20. If the mail server at priority 10 is unreachable, the sending server falls back to priority 20, and so on. Think of it as "first come" ranking, not a scored ranking.
Multiple MX records provide redundancy — if your primary mail server is temporarily down for maintenance or an outage, mail doesn't bounce; it queues and retries the backup server. This is standard practice for any domain that can't afford to lose incoming email during downtime. Records with equal priority values are used interchangeably in round-robin fashion, providing basic load balancing.
A domain using Google Workspace typically has MX records like: 1 aspmx.l.google.com, 5 alt1.aspmx.l.google.com, 5 alt2.aspmx.l.google.com, 10 alt3.aspmx.l.google.com, 10 alt4.aspmx.l.google.com — Google's own infrastructure with several fallback tiers built in.
Our Bulk MX Record Lookup shows every MX record and its priority for as many domains as you need at once — handy for auditing a portfolio of domains or verifying a mail migration went through cleanly.