The roles are different

An MX record identifies the mail exchanger for a domain. An A record maps a hostname to an IPv4 address, while an AAAA record maps a hostname to an IPv6 address. When delivering mail, a sending system can use the MX result and then resolve the target hostname to an address. This is why an MX record should normally contain a hostname rather than an IP address. The DNS layers provide routing and address resolution separately.

Example configuration

A simple setup might publish an MX record for example.com pointing to mail.example.com. The mail.example.com hostname then has an A record pointing to the server's IPv4 address. If IPv6 is used, it may also have an AAAA record. Changing the server IP can therefore be done by updating the address record while keeping the MX hostname stable, subject to DNS caching and operational planning.

Common mistakes

Publishing an MX record directly to an IP address, creating an MX target without an address record, or leaving an old MX target after migration can all cause delivery problems. Another mistake is changing website A records while assuming the email routing will change automatically. Keep website and email DNS inventories separate even when they share the same domain.

Troubleshooting

Inspect authoritative MX records first. Then resolve each MX target and verify that the returned address is the intended mail server. Finally test SMTP connectivity and inspect the receiving server's logs. If different networks return different DNS results, compare TTLs and authoritative data before making additional changes.

Migration checklist

Record the current MX and address records, prepare the new receiving host, verify its SMTP service, update DNS, and monitor both old and new systems during the transition. Test actual inbound delivery rather than relying only on a successful DNS lookup.

Key takeaway

MX answers “which host receives mail for this domain?” while A or AAAA answers “which address does that hostname use?” Understanding the distinction makes DNS troubleshooting much more systematic.

Practical checklist

• Record the exact hostname, domain, IP address or SMTP response involved in the issue.
• Change one variable at a time and keep a short change log.
• Verify the result with a real test message and inspect the relevant DNS or SMTP evidence.
• Document the final configuration so the next migration or incident starts with known-good information.

Frequently asked questions

Is there one setting that guarantees successful delivery?

No. Email delivery depends on the complete sending path, including infrastructure, authentication, recipient policy, message handling and operational practices.

Should I change several settings at once when troubleshooting?

Usually no. Controlled changes make it easier to identify the cause and confirm whether the fix actually worked.