Email client that restricts certain accounts to particular connection types, e.g. company WiFi at work, 3G/GPRS for personal
If you have root access then you could use DroidWall to give different apps, including email clients, access to WIFI and or mobile data. This would require you to use a different client for each account and wouldn't automatically differentiate between WIFI at work or at home. :o/

(It's a pretty rough work around but the best I could think of...)