ssh -L 2143:localhost:143 -L 2025:localhost:25 username@192.168.100.4

Thanks
Robert

To Read the full article go over to Hak5 and read the whole thing.

http://www.hak5.org/episodes/episode-416

What you’ll need

* An SSH server to act as your proxy.

http://www.g-loaded.eu/2006/11/24/auto-closing-ssh-tunnels/

The best way - Tunnels that auto-close

SSH Without a Password

http://www.csua.berkeley.edu/~ranga/notes/ssh_nopass.html

The following steps can be used to ssh from one system to another without specifying a password.
Notes:

Syntax for running command on a remote host:
ssh [USER-NAME]@[REMOTE-HOST] [command or script]

http://www.cyberciti.biz/tips/linux-running-commands-on-a-remote-host.html

Where,