When you use the SMTP Diag tool
from our site you see that the banner you are displaying publicly is masked by asterisks:
Connected to smtp.example.com.
The reverse check takes the banner and the PTR record for the IP and sees if the domain is listed. Since all we get publicly is the asterisks, the comparison fails and you get the warning.
Many administrators choose to mask their banner in hopes that by not giving an attacker a domain name, they might avoid something like a directory harvest attack. My personal opinion is that if you are using a single IP for inbound and outbound, then you are going to need put your domain in your PTR records for your outbound, then you might as well put it in your banner. However, this is personal preference and nobody should deny sending or receiving mail from your server just because you aren't throwing your domain in the banner.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 changesConfigure 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
Let us know if you have any other questions or concerns.