Mailinglist Archive: opensuse (1103 mails)

[Anders Johansson <ajh@xxxxxxxx>]

On Saturday 14 January 2012 12:59:10 Werner Flamme wrote:
> [14.01.2012 12:06] [Anders Johansson]:
> > On Friday 13 January 2012 07:32:49 Werner Flamme wrote:
> > > When reading <http://en.wikipedia.org/wiki/Blind_carbon_copy>, I do not
> > > get the impression that is is inteded to have this been solved by the
> > > receiving client. However, the text is vague, as are the RFCs.
> >
> > There are two recipient fields. One that is in the body of the email, and
> > one that is used when talking to the receiving mail server. The first is
> > typically referred to as "header to:" and the second as the "envelope
> > to:".
>
> You're confusing me by by putting together body and header of the mail
> as body. But OK, as a difference to the envelope, that's clear.
>
> > When you send an email, you connect to the receiving mail server, and send
> > the command RCPT TO: followed by all the addresses on that server that is
> > supposed to have the email.
> >
> > When you put an address in bcc, what this means is that the address is not
> > put into the header, so it is not in the text body of the email. It is in
> > the envelope to: but *only* when sending to that particular address. This
> > means that other recipients of the email don't know it also went to the
> > bcc address. They have no way of knowing about it. The information simply
> > isn't there, so the filtering cannot be up to them.
>
> As I understand this, the (first) server reads the RCPT TO: line and
> compares it with the to:, cc:, and bcc: lines in the header, since it
> must know how to forward the mail. Is this correct?

No, the bcc line is not visible to any server at any point. It is only used by 
the client. It goes through the list of addresses in the bcc field, and sends 
them one by one to the server in the envelope only. No mail server sees the 
bcc contents at any time

> But what does the next mailserver do? Example: userd@xxxxx sends a mail
> to his local mail server (outgoing mail relay) that is addressed TO:
> usera@xxxxx, CC: userb@xxxxx, and BCC: userc@xxxxx. This first mail
> server removes the BCC line, and sends the mail with the remaining TO
> and CC entries to the MX of c.com - this server may not compare the
> envelope recipient with TO: and CC: - or what? Do the servers compare
> with Bcc: only?

The mail server is not allowed to use the header fields for routing. Doing so 
is a major bug (we see it for example with certain older versions of Lotus 
Domino, they will resend emails based on header information, causing mail 
loops. This is a violation of the protocol)

The server is only supposed to look at the envelope information. The header 
To: and cc: fields should be plain text only and not used for relay or routing 
information in the SMTP protocol.

Anders
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