[Mimedefang] Email resend

[-]

--- On Thu, 12/10/09, Dave O'Neill <dmo at roaringpenguin.com> wrote:
> ...
> A Bcc: "header" is an artificial construct used by mail
> clients, and shouldn't ever appear in an actual
> message.  If mails had a Bcc header on-the-wire, it
> wouldn't really be a _blind_ carbon-copy anymore.

WRONG!  If a message has no other recipient-type headers (To, CC, resent-to, etc.), then the BCC header IS supposed to appear in the message with a blank data field.  This is to satisfy the requirement that at least one recipient-type header be present in the message.

RFC 5321, Appendix B, Headnote 1:

     "Each recipient address from a TO, CC, or BCC header field SHOULD
     be copied to a RCPT command (generating multiple message copies
     if that is required for queuing or delivery).  This includes any
     addresses listed in a RFC 822 "group".  Any BCC header fields
     SHOULD then be removed from the header section.  Once this
     process is completed, the remaining header fields SHOULD be
     checked to verify that at least one TO, CC, or BCC header field
     remains.  If none do, then a BCC header field with no additional
     information SHOULD be inserted as specified in [RFC 5322]."

RFC 5322, Section 3.6.3, indicates a couple of other appearances for the BCC header, all of which I consider as non-standard and have never observed (except the usage upon initial message submission).

Therefore, "wire-format" messages may contain a "BCC" header, and most often, it occurs with no data when no other recipient-type headers are present, but it may occur with addresses.  Such addresses may list all (not recommended) or may list only the specified BCC recipient receiving that copy of the message; the message having been split by the MSA and intervening MTAs in the delivery chain.

Your position that it "should never occur in wire-format messages" is patently wrong.