It seems that sendmail needlessly (?) removes duplicate To: and Cc: headers
from messages it feeds to procmail.  I'd prefer that it left them
untouched, as people (myself included) have made it an habit to have more
than one Cc: line.  Also, some of my mail-splitting rules match
mailing-list names in these fieds and, when sendmail removes the lines that
happen to contain the mailing-list name, I get the message in the wrong folder.

I've noticed that the queue file still contains duplicate headers, and,
when sendmail forwards messages via SMTP, it won't discard duplicates.  By
replacing procmail with a shell-script that cat all of its stdin in a
temporary file and then execed the actual procmail so that it reads from
the temporary file, I've noticed that what sendmail feeds to procmail does
NOT contain the duplicates, so it is not procmail that is removing duplicates.

I couldn't find any mention of this new (mis)feature in the release notes
of sendmail, nor any configuration flags to revert to the original
behavior, so this may well not be something specific to Red Hat Linux 7's
default configuration, but I thought I'd report it here just in case.

I've just verified that the problem does not occur with a hand-built
sendmail 8.11.1, so either the problem was fixed in 8.11.1 or it is
specific to Red Hat Linux.  Please verify.