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

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