We added the line
check_client_access hash:/opt/zimbra/postfix/conf/permitted_hosts
to our
/opt/zimbra/conf/postfix_recipient_restrictions.cf
file with 5.0.5. When we upgraded to 5.0.8 this line was removed from the file and permissions on the permitted_hosts file and its database were both changed to 550. This means that the zimbra user could no longer create a new postmap database if there was a change to the permitted_hosts file and the file was not being checked anyway because the line telling postfix to check this file was gone.

Obviously, I recreated my original steps and am working again. I would like to know if the file permission changes and the custom file check command belong somewhere else that will not get overwritten when we do upgrades.