In the world of email your IP reputation is everything. If you have been added to a Real Time Blacklist - chances are in a short space of time very few people will be able to receive your messages.
There are many tools online that will check for you - one we use on a daily basis in the office here is: http://mxtoolbox.com
All you need to do is open your favourite Web browser - enter the URL above and you are set.
To check just enter either your domain or IP address of your mail server. MX toolbox will very quickly report back on the state of your server.
If there are any RBLs listed in the report - you can click the “Details” button to go through and find out where the block is and, in most cases, what the cause of the block was.
If you have any form of management on your account - and you find your server has been blocked by an RBL - it is highly recommended you put in a support ticket and we will check over your server for you and find the cause of the spamming.