> I have a hard time getting the following situation sorted out
> and would appreciate any input to solve it.
> I'm in a firewalled LAN which provides a ssh-proxy to access
> outside machines which I have to use like so:
> 1) build tunnel
> ssh ProxyUser@SSHPROXY -L 2022:OUTSIDEBOX:22
> 2) make connection
> ssh -X OutsideboxUser@localhost -p 2022
> What I now wish to do is to access an outside mailserver
> (especially port 993) through this proxy and am stuck how to
> conceptually do this - build another tunnel through the tunnel?
> If anybody can nudge me in the right direction, I would be
> very grateful.

ssh ProxyUser@SSHPROXY -L 2022:OUTSIDEBOX:22 -L2993:OTHERBOX:993

Connecting to local port 2993 would connect you to your mail server while
keeping the existing tunnel for port 22.