[exim] UCEPROTECT Blacklists and why callouts are abusive

As we explained on our website, we consider callouts abusive, because they
can make your system part of an ddos against others.

If someone claimes to be you@yourdomain and sends out some million spammails

you will get a real feeling, why you should not use callouts.

Ok your system will have to deal with tons of bounces, but additional with
all those lamerz using sender callouts.

The problem is not that ONE connecction which you are doing. The problem is,
that you and millions of others
are trying to verify one address, which leads to a ddos against the targeted
system.

This is the reason why we are blacklisting anyone probing spamtraps of the
project.

The only difference between verifyers and for e.g. TMDA-Abusers is that no
real mail is sent by verifiers.

Anyone using sender callouts shows that he is selfish and it does not matter to him, to be part of a ddos against third parties.