If you're running OpenSMTPD (such as an OpenBSD system),
here's how to return the favour to t-online.
In smtpd.conf, before any of your 'listen' statements, add:
filter dtag phase mail-from match rdns regex "\.t-online.de$" \
reject "550 5.7.1 you don't accept our mail, so we don't accept yours."
Next, on each of the 'listen' statements that apply to your
public-facing SMTP interfaces, add the phrase 'filter dtag'.
This will reject all mail coming from hosts with a PTR
record that includes a *.t-online.de domain name. (If you
find any, please drop me a note and let me know. Or maybe
post them to them here. It might be worth maintaining a
public list to people can write similar blocking rules for
their MTAs.)
The content of that regex might need to be expanded to include
other reverse domains they use.
Thanks to Florian Obser for pointing out the errors in my
first run at this.
--lyndon
_______________________________________________
mailop mailing list
mailop@mailop.org
https://list.mailop.org/listinfo/mailop
