A mail exchanger is a CNAME

What it means

example.net is an alias rather than a host with its own address. The standard forbids this, and while most senders cope, the ones that do not simply fail to deliver.

How to fix it

Point the MX at a hostname that has A or AAAA records directly, not at an alias.

Check your own domain

This page describes the condition. To find out whether your domain has it, run the MX test or the full checkup, which examines every record at once.

Understand it properly

This page covers one condition. For the whole picture, Why mail lands in spam, in the order worth checking, or start at the Health Library.

Where this comes from

We judge this against RFC 5321 section 5.1. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.

Other MX conditions

• No MX records
• Domain declares that it accepts no mail
• MX record points at an IP address
• Only one mail exchanger, on one address
• A mail exchanger has no address