procmail slow delivery

I'm having a problem with procmail delivery.  It takes
long time to deliver mail to users.  I install procmail with
"install-suid" option.  Here is the copy of .procmailrc in
user HOME:

# Please check if all the paths in PATH are reachable, remove the ones
that
# are not.
 
PATH=$HOME/bin:/usr/bin:/bin:/usr/ucb:/bin:/usr/local/bin:.
MAILDIR=$HOME/Mail      # You'd better make sure it exists
DEFAULT=$MAILDIR/mbox
LOGFILE=$MAILDIR/from
LOCKFILE=$HOME/.lockmail
 

# Anything that has not been delivered by now will go to $DEFAULT
# using LOCKFILE=$DEFAULT$LOCKEXT
        :0:$HOME/.lockmail
        $DEFAULT

I'm running procmail_v3.11pre3 under Solaris 2.5.

Here is the output from the "procmail -ver "command:

# /bin/procmail -v
procmail v3.11pre3 1995/05/17 written and created by Stephen R. van den
Berg
                                
berg(_at_)pool(_dot_)informatik(_dot_)rwth-aachen(_dot_)de
 
Submit questions/answers to the procmail-related mailinglist by sending
to:
        procmail(_at_)informatik(_dot_)rwth-aachen(_dot_)de
 
And of course, subscription and information requests for this list to:
        procmail-request(_at_)informatik(_dot_)rwth-aachen(_dot_)de
 
Locking strategies:     dotlocking, fcntl()
Default rcfile:         $HOME/.procmailrc
System mailbox:         /usr/spool/mail/$LOGNAME

Thanks in advance.
Matt