This problem is *NOTHING* to do with fetchmail. It is a problem with
your local IMAP/POP server and LDA. Using procmail if you use "-f -" as
arguments it'll generate the "From " line for you - details are in the
procmail man page.
Let me first thank you for your help. With luck this may provide the last
piece of the puzzle for me to get my fetchmail working reliably. I hadn't
spotted that option in procmail(1).
Ouch. As seems to be the way, this solution opens another problem.
procmail now produces the message
procmail: Lock failure on "/var/mail/michael.lock"
Unfortunately, it seems I now need to open the complicated box labelled
"e-mail file locking", and I don't know how my system does it.
I'm on FreeBSD 4.9 running sendmail with mail delivery to old fashioned
Unix mailboxes in /var/mail.