[chmike]

Spamhaus is blocking by IP which can be an smtp server or a client. The SMTP protocol does not allow to distinguish a sending SMTP server from a client.

By using a VPN, you "randomize" the IP address and thus make spamhaus and equivalent services useless. I created my own IP blacklist and tracked it.

The only method I found to filter my spammers is to reject mails from hosts without a name. This eliminated 80% of spam, but it won't last long.

The mail system is completely broken.

[sylware]

use grey listing

[chmike]

I have spammers retrying 20 times before giving up. This protection is well known and easily circumvented be spammers.

[sylware]

but it filters a lot already because many do retry 20 times in less than 20 minutes.