Re: [exim] "25 lost" is giving me useful clues

> > What this is telling me is someone at 157.0.116.189 is making
> > connections to my mail server - presumable to see if they can detect the
> > accounts of users on my machine?

It tries to guess passwords of users on your machine
(brute-force password cracking).
This code catches both using guessed passwords for spamming
and the guessing (auth cracking):
https://github.com/Exim/exim/wiki/BlockCracking