Can't run postfix on Mountain Lion due to missing system_user_maps.db When I start postfix, I see in /var/log/system.log the following error:

error: open database /etc/postfix/system_user_maps.db: No such file or directory

How should this file be created so that postfix can start properly?

I tried doing touch on this file, but I get the error 


postfix/cleanup[871]: warning: hash:/etc/postfix/system_user_maps is unavailable. open database /etc/postfix/system_user_maps.db: Inappropriate file type or format`


Is there a postmap command that sets this up?
I figured it out. You need to not only touch /etc/postfix/system_user_maps but also run sudo postmap /etc/postfix/system_user_maps to create /etc/postfix/system_user_maps.db. Then postfix will start up.