[Exim] user/group transports

Hello all,

If in a transport (exim4) a mysql query returns a name instead of a
uid/gid, will exim look that up through getpwnam() or whatever it is?

I took a look through the manual and didn't seem to find a clear answer on
this. Just wanted to confirm before I make a really huge change on my mail
server.

Thank You,
James Harr <james@???>