As more and more spam is coming through, and the RBL, blacklists etc. are starting to loose the SPAM War, I decided to tighten the restrictions on Mail-Acceptance. Not only does the system from now on only accept mails from systems with correctly configured FQDN in the EHLO/HELO SMTP communication initiation, but also TLS has been setup to be way more restrictive as I noticed many systems - bots - use TLS to connect to the Mailserver - I force the system to perform a very strict certificate check.

Spam-Rate has dropped since then by 5%.
Note that already more than 75% of the E-Mails received by this Mail-Server are SPAM.