What to do to minimize chances of being blacklisted by DNSBL databases...

Whatever is described below assumes that your server is not an open relay, it is protected by enabling SMTP authentication (Security - AntiSpam - SMTP Authentication is enabled), and none of your users does actual spamming...

To test whether your IP address is blacklisted, use the this page at WhatIsMyIPAddress.com.

If your IP address belongs to a DSL or cable provider, then you are already blacklisted by some DNSBL databases. They consider these IP addresses as ones with low "reputation".

Some DNSBL services blacklist entire ISPs. Make sure to use ISP in "good standing".

If one of IP addresses does spamming, some DNSBLs may blacklist that IP address, and at the same time - their neighbours too...

If you are blacklisted becase of above mentioned problems, there is only one solution: change ISP, and get different IP address with good "reputation".

Here is what you can do to avoid being blacklisted if your ISP and your IP address are not blacklisted because of above listed reasons:

• In your mail server settings, at Options - Server Options - General - Local Host use fully qualified domain name, for example, use mail.myoffice.com.  It is the value how your mail server identifies itself when connecting to remote servers.  Also, it would be useful if you ensure that mail.myoffice.com exists, translates to an IP address, and that IP address matches the IP address your server is visible from outside world;
• Ensure your IP address has reverse PTR record. It means, the IP address your server is visible to the outside World translates to a valid domain name.  It would be very useful, if that domain name matches the local host value you are using on your mail server (see above)...  You have to ask to do these adjustments your ISP, one which provides you with IP address;
• Use Sender Policy Framework (SPF) for domains, on behalf of which your mail sends mail out.  SPF publishes addresses of servers, which are authorized to send mail out from a domain, and existance of SPF indicates, that you care about the reputation of your domains. For more information about SPF go to OpenSPF.org;
• Use DomainKeys.  See the help file of your mail server for more information.

Back to the list of documents

Back to the Mail Server .NET FAQ

Back to the Mail Server .NET