Why is my IP blocked by Spamhaus or SORBS

I am trying to deliver email directly through your E-Mail Server, but I get back an error message saying that my IP is blocked for some reason. Is this a bug in your software?

This is not a bug in our E-Mail Server. This message actually comes from the target SMTP server. Our server is only passing you that message as is without changing or adding anything.
The problem is, most modern ISP's do not want to receive any email from dynamic IP addresses. They are governed by very simple logic. If you have dynamic IP address, allocated to you by your ISP, you must be a regular home computer user. We do not want home computer users to send us email directly. We want them to use their ISP's email server. This is all nice and logical, but what if your ISP places a lot of limitations on your email. Some providers allow you to send only 50! messages per hour. I cannot imagine how I would run a home business with this limitation. So the best way for you to avoid blocking is make sure you have a good clean static IP address that is not listed in any black lists. Here is a procedure on how to go about obtaining it:

  1. Call your ISP and ask them to provide you a fixed static IP address instead of your dynamic one. This depends on your ISP and even within ISP, some support people will be knowledgeable and some are not, so gear up with some patience here. Most ISP's do not mind giving you a static IP for your needs, some have specific policies on how to justify one and some might ask you to pay some extra for it. My ISP wanted me to pay 6$ per month extra, but after some extensive bargaining, I managed to do it free of charge.
  2. Now, you must check that your IP address is indeed static and is not already listed in any black lists. The easiest way to do it is by going
    here: http://checker.msrbl.com/v/1/
    These are tools, that will query multiple large RBL and DNSBL lists for you and return the results grouped together.
  3. You should also make sure that your static IP has a good reverse DNS resolution, because some mail servers will check for that as well. To do that, go
    here: http://remote.12dt.com/
    or here: http://www.zoneedit.com/lookup.html
  4. Finally, please check that your HELO string that your server emits is the same as your reverse DNS resolution in the step above. This is needed, because many SMTP servers will check that your HELO string corresponds exactly to your reverse DNS record. The logic behind it is that if you are honest about what domain you are coming from and say it openly in the HELO string, they have more reason to trust you. Most SMTP servers will have a configuration variable for this HELO string. Here is how it looks like in our E-Mail Server.

    In our server we also make it auto discover your correct HELO string by default or you can do it yourself, by pressing the button "Try to find my fully qualified domain name"