Hey friend,

Personally I enjoy rspamd for filtering spam with Postfix:
https://rspamd.com/

That said, there’s only one way that I can think of for a “one size fits all” fix on this. Are they sending these emails from a specific server, or through a large mailing service? If they’re sending from one server, grab that server’s IP from your logs and black hole it like this:

ip route add blackhole 1.1.1.1
(Replace 1.1.1.1 with their server IP)

If it’s always the same sender, I’m pretty sure this still works, despite it’s age:
https://www.cyberciti.biz/faq/howto-blacklist-reject-sender-email-address/

Jarland

Hi, this question keeps popping up in my google searches and even though it is a bit old I think it deserves a longer answer. Basically, your server should drop emails from IP addresses that connecting to it claiming to send email from you.

How? Use SPF records on your domain name. SPF records indicate which hosts and ip addresses are effectively used by you to send email as that domain name. Implementing such an SPF record, and the corresponding SPF checking on incoming email on your server will help with your problem. And it will also enhance your servers ability to drop spammy email. This guide explains EVERYTHING: https://workaround.org/ispmail