What does MX priority mean?

The lower the number, the sooner a sending server tries that host. Hosts with equal priority are tried in random order, which spreads load.

Why does a missing MX record still receive mail?

When no MX exists, RFC 5321 tells senders to deliver to the A or AAAA record of the domain itself. Many receivers and filters treat that fallback as a weak signal, so publish an explicit MX.

Can an MX point to a CNAME?

RFC 2181 says it must not. Most modern senders cope, but some older MTAs refuse it, and it costs an extra lookup per delivery. Point MX records at A or AAAA names.

MX lookup

An MX (Mail Exchange) record is a DNS entry that tells senders which server accepts mail for a domain, and in what priority order. This tool finds a domain's MX records, in the order senders will try them, and checks whether each one actually resolves.

What this tool checks

The tool asks public resolvers for the domain's MX records, sorts them by priority, and then resolves each exchange name to its IPv4 and IPv6 addresses. It flags four things senders care about: no MX at all, an exchange that is a CNAME, an exchange with no address, and an address in a private range.

How to read the result

The first column is the preference value. Senders start with the lowest number and move down the list only when a host does not answer. Two hosts with the same value share the load. The addresses on the right are what a sending server will actually connect to on port 25.

Where Spamjadoo sits

When Spamjadoo is deployed for a domain, the lowest-priority MX points at a Spamjadoo node. Every connection to that host goes through the protocol checks described on the how it works page before any message content is accepted, and clean mail is relayed to the real mail store behind it.

Questions people ask

What does MX priority mean?: The lower the number, the sooner a sending server tries that host. Hosts with equal priority are tried in random order, which spreads load.
Why does a missing MX record still receive mail?: When no MX exists, RFC 5321 tells senders to deliver to the A or AAAA record of the domain itself. Many receivers and filters treat that fallback as a weak signal, so publish an explicit MX.
Can an MX point to a CNAME?: RFC 2181 says it must not. Most modern senders cope, but some older MTAs refuse it, and it costs an extra lookup per delivery. Point MX records at A or AAAA names.