procmail and mail file locking

Does procmail default lock the local delivery mail file as I have been told postfix and other MTAs do? If I run procmail -f $MAILTO where procmail is getting the mail file from STDIN. Or do I add something like the following to my script: exec 100>/var/spool/mail$USER.lock || exit 1 flock -w 120 100 || exit 1 And do I also need -d $MAILTO on the above procmail call? thanks