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Howto block mailservers using uncommon TLDs in hostname through Postfix

Blocking or blacklisting entire Top Level Domains (TLDs) used for hostname in email server setup can be a very effective solution to stop low reputation mail servers delivering mails to your email system(s). As most email providers use common TLDs like .net, .com or .de in their email setup, you can selectively block new or low reputation TLDs and this way reducing a lot of unwanted emails. If you are looking for a tutorial to blocking/blacklisting sender (users/clients) using specific TLD, this tutorial is the right one for you: Howto Block Entire TLDs in Postfix for Senders.