Understanding MX records

What an MX record looks like

example.co.za.   3600  IN  MX  10 mail1.example.co.za.
example.co.za.   3600  IN  MX  20 mail2.example.co.za.

Each MX record has a priority (also called preference) and a mail server hostname. Sending servers try the lowest number first. If it's unavailable, they try the next one. Records with the same number share the load.

MX records for popular email services

Your email provider gives you the exact values — always copy them from their documentation, because they change over time and vary by account. As a pattern: Microsoft 365 uses a single MX pointing at a *.mail.protection.outlook.com hostname; Google Workspace uses smtp.google.com (older setups list several aspmx hosts); cPanel hosting typically points the MX at the domain itself or a mail. hostname on the server.

Mistakes that stop email arriving

• No MX record after a nameserver change. The single most common cause of “we're not receiving email” after moving DNS.
• MX pointing to an IP address. The value must be a hostname, and that hostname needs an A/AAAA record.
• MX pointing to a CNAME. Not allowed by the standards; some senders will refuse it.
• Old MX records left behind after switching provider, so some mail goes to the old system.
• Missing trailing dot in DNS panels that append your domain automatically.

MX records and spam filtering

MX records decide where mail is delivered; they don't prove who may send it. Sending authorisation is handled by SPF, DKIM and DMARC. Check all four together with the Email Deliverability Checker.

Domains that don't receive email

If a domain should never receive email, you can publish a “null MX” (0 .) to tell senders not to try, and an SPF record of v=spf1 -all so nobody can send as it.

Running an MX lookup

dig example.co.za MX +short
nslookup -type=MX example.co.za

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