qmail and plesk and many in queue but not yet preprocessed

[Jeremy C. Reed]

I have an old plesk system where it continually has many "messages in 
queue but not yet preprocessed" and the messages in queue gets more and 
more behind. It accpets mails, but doesn't handle them quickly.

It doesn't have any noticable bottlenecks.

It appears to start doing this when ever the load average gets above 
three. When I stop jobs and the load goes below, it starts delivering 
again.

My questions:

- how to get qmail to report why the mail is "not yet preprocessed"? (This 
is not indicated in my logs.)

(In the past I have had same problem due to lack of disk space -- but 
qmail never logged about that either.)

- any config to look at that tells qmail to not preprocess based on some 
condition?

Since this is plesk, it is not a DJB-standard system.

It has qmail-send running:

It uses xinetd to to handle smtp connections which then runs:

/var/qmail/bin/tcp-env  -R /var/qmail/bin/relaylock \
/var/qmail/bin/qmail-smtpd /var/qmail/bin/smtp_auth /var/qmail/bin/true \
/var/qmail/bin/cmd5checkpw /var/qmail/bin/true

Any suggestions to look at would be appreciated.

  Jeremy C. Reed

p.s. We are migrating from this system, but in the meanwhile I need to 
keep it alive.