[Exim] inbox encryption

Hello all,

the company I work for wants to build up a new mail server under
Linux. They're considering using exim or sendmail (the latter is in the
SuSE-Distribution, which is quite famous in Germany) as server and some
POP3 and maybe IMAP server to allow users fetching their mail.

Now my boss asked me whether it is possible to either encrypt all
mailboxes or log all accesses to it, so that root isn't able to read any
mail. Under MS Exchange this is possible, he says (or at least you ought
to install some extra program to view the mailboxes), so on the new server
the administrator shouldn't be able to read messages, too.

I told him this is nonsense, for (almost) anybody else may read these
mails if they're going through the internet and our customers should
better use tools like pgp or gpg or the like. But he want's it
nonetheless.

I've thought of inserting an encryption filter to the appendfile transport
and doing the same on the mail server, but then you have the key lying
somewhere around.

Does anybody has some ideas about that?

Robin Putzar