A while ago, I posted an inquiry about the occurence of empty
messages, with "Content-length: -1" headers, when using sendmail
8.6.12 (and 8.7), with procmail v3.11pre3 for final delivery.
It appears the problem was really with an MUA or two.
It looks like the problem has been eliminated, for all our known
MUA's, across a number of vendors' platforms, by shutting off the
Content-length header altogether, by using the "E" mailer option in
the sendmail.cf on the hub, and the "-Y" option to procmail.