[imp] setting default mail server

[Liam Hoekenga]

> Someone please correct me if I'm wrong but I beleive putting
> 'preferred' => 'true';
> inside one of the server definitions in servers.php will set the default,
> even if your hiding the server list.

Actually, I think it's a comma separated list of the webservers (whatever
SERVER_NAME returns) that that IMAP server should be the default for.

At least.... that how we're using it here, and it's working.

Liam