Hmm...
My servers indicate that this is a new configuration option that wasn't present in 1.660 but is in 1.661
# /usr/local/directadmin/directadmin version
DirectAdmin v.1.660 351bc3cb3edd62304d5d7a96b59b79211e607eff
# /usr/local/directadmin/directadmin c | grep log_email_ftp_password_change...