[Mimedefang] Rejecting e-mails with blank CC: and Reply-To:

[kd6lvw at yahoo.com]

--- On Wed, 4/11/12, Scott Nelson <sbnelson at thermeon.com> wrote:
> > The only header which is permitted (and in fact required after MSA
> > processing) to have a blank data field is "BCC:"  Therefore, to
> > permit these headers above to be blank violates the message format
> > standard.
> 
> I would have thought that BCC would be stripped off the message altogether...

You thought wrong.  When there is no "To:", "CC:", or other recipient headers (e.g. "Resent-To:") but "BCC:" was used, an empty "BCC:" header is supposed to be added back to the message (such indicates that ALL recipients were BCC'ed).

RFC 5321:
"Appendix B.  Generating SMTP Commands from RFC 822 Header Fields

"  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, Section
       3.6.3]."