Question : What does "Reverse DNS does not match SMTP banner" mean?

"Reverse DNS does not match SMTP banner" is a warning shown by mail testing tools such as MXToolbox. It means that the name your mail server gives when it greets other servers is not the name that the reverse DNS record of its IP address returns. The warning rarely blocks email by itself, but some receiving servers treat the mismatch as a sign of a careless setup, so it is worth fixing when you run the mail server yourself.

What the warning compares

• The SMTP banner: the first line a mail server sends, starting with 220. It contains the server's hostname, which the server repeats when it introduces itself (see HELO and EHLO).
• The reverse DNS (PTR) record: the DNS record that turns the server's IP address back into a name.

The tool expects the same name on both sides, for example mail.yourdomain.com.

How to check it yourself

1. Type nslookup followed by your server's IP address. The name in the answer is the reverse DNS record.
2. Connect to the server and read the line that starts with 220. Our guide on how to test an SMTP server gives the command.
3. Compare the two names. They should be identical.

Would you rather not manage reverse DNS at all? With the Mailpro SMTP relay service, your website or app sends through Mailpro's servers, and keeping them correctly set up is Mailpro's job.

How to fix the mismatch

1. Choose one hostname for the mail server, for example mail.yourdomain.com, and create an A record that points it to the server's IP address.
2. Ask the company that owns the IP address (your hosting, cloud or internet provider) to set the reverse DNS record to that hostname. This record is set by the owner of the IP address, not in your domain's own DNS zone.
3. Give the server the same name for its greeting. In Postfix this is the myhostname setting; in Microsoft Exchange it is the FQDN of the send connector.
4. Run the test again. DNS changes can take a few hours to show.

When you can ignore the warning

• You use a hosted mailbox such as Google Workspace or Microsoft 365. The servers belong to the provider and you cannot change their names.
• You send through an SMTP relay. The relay's servers deliver the email, so their reverse DNS is the provider's responsibility.
• The server you tested only accepts mail from your own applications and does not deliver to other mail servers.

For reaching the inbox, SPF, DKIM and DMARC on your sending domain weigh more than this warning. See how they work together on our email deliverability page.