You can write to Mack at this address:
Mackenzie Rosman
c/o The WB Network
3701 Oak St.
Building 34R
Burbank, CA 91505
USA
Mackenzie Rosman
7th Heaven Production
3401 Exposition Boulevard
Santa Monica, California
90404
USA
I haven't written to any of these addresses (yet), but if you have a got and a reply, please let me know!