[exim] LDAP/Kerberus/Radius question.

Hi,

i konw, it's a bit too common , but as the question for GSSAPI reminded
myself, i never got why ldap is used in some exim setups.

As i understand it, if you want to authenticate users from multiply
points in your network, you can setup an authserver with ldap,kerberus
or radius and only need to administrate the passwords there.

Question:

Where is the big advantage over ...

- a _local_ mysql database auth ?
- a mysql database server _at all_ ?

best regards,

Marius