SSH Tunnel Help

I have a shell script that creates a SSH tunnel when I check my email.
I am using OpenSSH (protocol 2). Here are some things to know about
before you look at the script: first, I can ssh without entering a
password, and secondly in evolution I have it set to check mail on the
localhost with ports 8110, and 8025. Here is what the script looks
like:

#!/bin/sh

# set up SSH tunnel
ssh -L 8110:mailserver:110 -L 8025:mailserver:25 username@host.com
'sleep 600; exit' &

# start up Evolution
evolution

The problem with my script is that the SSH tunnel is only good for 10
minutes. So if I read through my email and it takes me 15 minutes,
then I decide to send email or check email again, it won't work
because of the SSH tunnel being closed. Is there a better way to do
this? Is there a way I can make a shell script to create the SSH
tunnel, start evolution, the when I close evolution, the SSH tunnel
will close. I was thinking that it might be possible by having it
check to see if the evolution process id is running or not. Let me
know how I can do this? If anyone has any better ideas about this let
me know. Thanks.

Phusion