Your Server is getting blocked because of incorrectly configured reverse DNS or S25R rules.

After setting up your mail server it is important to insure that your DNS entries are properly configured in order to not have your mail rejected by many of the email filtering service providers or ISP's.

Your IT support company should set this up for you, however many don't pay attention to the details.  The issues involve Exchange Servers in which the DNS server's PTR records are not correctly configured.

Many times the IT company will setup a forward record which is something like pointing to the IP number of your server  The problem lies in the reverse of the IP number.  The ISP providing you DSL/T1 etc usually has something configured   for reverse DNS that looks like or  As you can see these reverse DNS entries have no association with and many Internet Service Providers and email providers, such as MSN, AOL and Hotmail, block spam by using reverse DNS lookups on incoming email server.

The proper setting for the example we have of would have a reverse DNS entry of pointing to  Your mail server will now comply with the mail server standards and you won't get blocked becuase of anti-spam policies such as or S25R.

If you configure your server properly you will prevent yourself from getting rejected email messages utilizing these policies.

if you have problems with your mail server Innovative Internet Solutions can fix your problem.

You can contact us here.

Further information about the Official Internet Protocol Standards can be found here as well as here.