mail servers using an enhanced client, sender and helo
restriction configuration.
The configuration has been adapted using this blog post:
https://www.webstershome.co.uk/2014/04/07/postfix-blocking-spam-enters-server/
Basically mail servers having invalid configuration (as e.g. sending
from and dynamic IP or a misconfigured hostname) will have their
mails rejected.
Additionnally three RBL servers are used to detect spam sending
IPs: dnsbl.sorbs.net, zen.spamhaus.org and bl.spamcop.net.
The results of a 12h test drive using a 100+ daily spam
mail account (SpamAssasin was always enabled, just counting
delivered mails to inbox not counting what SA detected):
- Before: 34 incoming mails
- Afer change: 6 incoming mails (82% reduction)
Fixes#161.
