For a while my solution was to SSH into my work computer and forward the X server so I could launch Thunderbird remotely. This works, but is slow and takes several minutes just to launch. I then have to sync the mail directory back to the laptop as well.
My next solution was to have an alternate VPN configuration that forwarded everything just for when I knew I needed email (or could switch to when I did), but I had a better idea. I couldn't just put the exact IP of the mail server since the VPN routing only allows ranges. Instead I set the range to /31. This includes the IP before and after, but I doubt that will be a problem.
In the end I get work SMTP connections at home and I still get to keep almost everything else off the network. Win/Win.