fetchmail + sendmail + procmail A lot of DNS query

Hi all,

I'm using Fedora Core 5 with sendmail configured as distributed. No
changes are made to sendmail config files.

I started using fetchmail to retrieve mail from a lot of pop3 servers,
and configured procmail to pass messages to bogofilter to mark as Spam
or not Spam.

It works well but sometimes is very slow.

I started analize why, and I see that a lot of messages are queued by
sendmail (mailq) and a lot of processes are used by sendmail and
procmail.

Also I see with tcpdump a lot of DNS queries but I don't know why this
appens.

my fetchmailrc is like that:
poll pop3server POP3 uidl tracepolls username "user" passwork "pass";

my .procmailrc is

PATH=$HOME/bin:/usr/bin:/usr/ucb:/bin:/usr/local/bin:.
MAILDIR=/var/spool/mail
#DEFAULT=$MAILDIR/$USER
LOGFILE=/var/log/procmail
LOCKFILE=$HOME/.lockmail

#BOGOFILTER_DIR=/var/spool/bogofilter

#### backup ####
#:0c:
#mail.backup
####
:0fw
| bogofilter -p -l -e --spam-header-name=X-Ambrogio-bogo

:0e
{
        EXITCODE=75
        HOST
}

I don't know sendmail configuration syntax, so I can't analyze what
appens.
Someone can explain me what appens, and why I have a lot of dns queries.
What I have to do to reduce this network trafic (maybe use X is y here
in fetchmailrc).

Tnx a lot
 Ambrogio