Mickey writes, "I'm being blocked by AHBL. I own a tax and accounting firm. We send out two newsletters per year to our existing clients using an ESP. We give our clients every opportunity to be removed from the list if they so choose. We do not and have not spammed ever. How did I get blocked by AHBL? No one is able to send me email. Please help. If I did something wrong let me know what. I have no clue and I need my emails working again."
Mickey, if nobody can send email TO you, that strongly suggests that something is up with YOUR mail server. When I tried to send you email at your domain, the message bounced back to me with this error message: "550 5.7.1 18.104.22.168 has been blocked by AHBL."
What this means: Your mail server, or your ISP's spam filtering system, is configured to use the spam filtering blacklist called AHBL. Unfortunately, that blacklist announced that they were shutting down, way back in April 2014. At the end of 2014, the publisher of AHBL moved the blacklist to a sort of "wildcard mode," meaning that anybody who was previously using the AHBL blacklist as a spam filter is now blocking all mail.
That means you -- your mail server, set up by you, your IT consultant, or your ISP, have to go into your mail server's configuration settings and remove any references to AHBL. Once that is done, you will be able to receive mail again.
All mail server administrators should remember to check their mail server spam filter settings periodically. When's the last time you checked to see which blacklists you are using? Are you sure all of those blacklists are still active and publishing? There's a section over on my DNSBL.com blacklist information website all about dead DNSBLS -- make sure you're not using any blacklist shown there, or you could run into troubles like this.