Why Does Mutt Delay Postings?

["Thomas H. George" <tom@tomgeorge.info>]

If, when fetchmail finishes downloading a batch of mail, I immediately
run mutt it displays only a few messages - and these may actually be
from a previous download.  In time - measured in hours, not minutes - a
re-run of mutt will display a large batch of messages retrieved by
fetchmail much earlier.

As far as I can tell no messages are lost, there is just a significant
time delay.

I have reviewed the .fetchmailrc, .muttrc and the exim4.conf.template
but see no reason for this delay.

Has anyone had the same problem?  If so is a solution known?

Tom George