Mechanism specific option
When using the rimap mechanism, this option describes the remote
server to forward authentication requests to.
Hostname can be a hostname (imap.example.com) or an IP address
(192.168.0.1).
The remote host is contacted on the imap service port.
A non-default port can be specified by appending a slash and the port
name or number to the hostname argument (192.168.0.1/14343).
Another mechanisms may use some config files that should be set up with
this option.