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.