What does the Warning – Reverse DNS does not match SMTP Banner mean? – SMTP Diagnostic Tool

We wanted to give a bit more insight into the Warning from our SMTP Diagnostic tool about ‘Reverse DNS does not match SMTP Banner’.

The short answer is that the reverse IP address name is not contained in the server HELO or EHLO banner. In the example below, the string “someotherdomain.com” is not found anywhere in the server banner, which is reporting “example.com“. This is only a warning, and in some cases you may have no control over this. However, if you have the ability to make these match, you should. Some mail servers look for this and use it to mark messages you send as questionable. Most mail systems will not reject your messages outright, but this may effect your spam score increasing the likelihood your messages will be marked as spam.

In other words, it is a best-practice you should endeavor to follow. It doesn’t mean you are a bad person or won’t be able to send email.

220 mx.example.com StrongMail SMTP Service at Wed, 09 Sep 2009 17:00:01 -0700

Not an open relay.
0 seconds – Good on Connection time
0.156 seconds – Good on Transaction time
OK – 1.2.3.4 resolves to mail.someotherdomain.com

If you are not sure where to access your SMTP banner in your mail server, read below for some helpful hints. We do not advise making ANY changes to your mail server if you are not the system administrator or confident in making these changes.

Configure SMTP banner Exchange 2003

  1. Open Exchange system manager.
  2. Expand your administrative group (”First administrative group” by default).
  3. Expand Servers.
  4. Expand “YourServersName”.
  5. Expand Protocals container.
  6. Select SMTP container.
  7. On the right window, right click the Default SMTP virtual Server (Or the name you set your SMTP Server) and select Properties.
  8. Select the Delivery Tab.
  9. Click the Advanced button.
  10. Under the Fully Qualified Domain Name (FQDN) type mail.yourdomain.com (The A/Host record you created in DNS for your mail server)
  11. Click Apply and OK again to accept the changes

Configure SMTP banner Exchange 2007/2010

  1. Open the Exchange management console.
  2. Select the Organisation Configuration container.
  3. Select Hub Transport container.
  4. On the right select the Send Connectors tab.
  5. Right click your send connector and select properties.
  6. On the General tab under the Set the Fully Qualified Domain Name (FQDN) this connector will… type the A record domain name you created. Which in our case is mail.yourdomain.com. Click OK.
  7. Under the Server Configuration container click the Hub Transport container.
  8. In the Right window Select the properties of the Receive Connector under Receive Connectors tab.
  9. On the General tab under the Set the Fully Qualified Domain Name (FQDN) this connector will… type the A record domain name you created. Which in our case is mail.yourdomain.com. Click OK.

To verify these changes we would recommend using our SMTP Diagnostic Tool again.

7 thoughts on “What does the Warning – Reverse DNS does not match SMTP Banner mean? – SMTP Diagnostic Tool

  1. Maurits

    Thanks for an excellent tool!

    When displaying the warning in question, it might be helpful to include the actual value of the SMTP banner in the diagnostic output. Currently it just warns that it doesn’t match the reverse DNS.

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    Reply
  2. John

    Does it show the banner? I must be blind too, because I don’t see it. I changed my banner info in the SMTP properties of my Exchange 2003 server, and then updated all PTR files. I’m still getting the warning but I don’t know what the banner is currently showing.

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    Reply

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