The new user/group names for exim 4 are unreasonably long
(and contain an ugly capital to boot). They get truncated
in ps and ls listings, which is very annoying.

In fact, you must have had to use --force-bad-name or
similar to even get the standard tools to let you do this,
which might be taken as an indication that the username
would be frowned upon.

Also, whatever group is chosen for the exim4 user, would
it not be possible to make said user a member of group 'mail'?
Otherwise I'm going to have to hunt down all the random files
that the MTA needs access to and chgrp them.