@aral, I can't sign the web0 manifesto. The error message: https://pastebin.com/xdqLGKiL
The message links to this guideline for senders: https://www.gmx.net/mail/senderguidelines/
Is it time to switch the mail provider?

@Jonius @aral

except the spamhaus racket seems like sensible rules!

you need to add a reverse dns entry at your registrar, resolving from the ip of your mailserver to your domain.