You know those same hosts, providers, or whole networks, who get through your
spam filter and spam your users with the same content over and over again. By
building up your blacklist in Postfix, you can stop them from bothering you and
your users. We will explain how local blacklists work in Postfix and how to use
them with
whitelists
to have better control and reduce errors.
Check before you blacklist
Blocking other hosts must be a well-thought decision because blocking single
hosts, IP addresses, or even whole networks will stop all delivery attempts to
your mail servers.
If you use any blacklists for email services, whitelisting important Hosts,
single IP Addresses, and even whole networks is an essential task. By
whitelisting valuables email services to your users or even customers, you as
admin won’t reject important email communication.
Blacklisting in Postfix
If you use any blacklist service or has your
blacklist
in your Postfix setup, you will probably find similar logs:
root@server $ grep "blocked using" /var/log/mail.log
Dec 17 4:07:18 server postfix/smtpd[21213]: NOQUEUE: reject: RCPT from
unknown[1.2.3.4]: 554 5.7.1 Service unavailable; Client host [1.2.3.4]blocked using ix.dnsbl.manitu.net; Blocked - see http://www.dnsbl.manitu.net/lookup.php?value=1.2.3.4;
from=<x0h0ihbxazf@somedomain.example> to=<cp57ouwn7zm9@mydomain.example> proto=ESMTP helo=<[1.2.3.4]>
As you can see in this example, IP Address 1.2.3.4 was blacklisted by a
third-party service.
MailMum offers individual services for email administrators to monitor incoming
mail traffic and to control it by blocking IP addresses or even IP networks of
abusive systems using Real-time Blackhole List (RBL) technology. The admin has
full control over the listings by defining parameters, blacklisted (abusive),
and whitelisted (trusted) IP addresses. The defined rules may apply for the
whole account down to an individual server.
Mail System Today
Provided by several sources email traffic is up to 90% or unwanted emails
(called spam or junk). Controlling them through spam filters (like
SpamAssassin or Rspamd)
is hard as it is expensive by teaching, running, and maintaining them. Also,
this high load of unwanted emails wastes a lot of costly resources that must be
paid and run by specialists.
A name, domain, logo, and a draft website - this is the way
MailMum was born out of an internal project.
From a necessity to this service
MailMum was born out of a need to face problems with unwanted emails called spam
or junk. As filters like Spamassassin were
good, but spammers are human, their job is to figure out how to bypass them.
They will try and will find ways to reach your inbox.