barmar@mit-eddie.UUCP (Barry Margolin) (08/22/85)
In article <560@neuro1.UUCP> sob@neuro1.UUCP (Stan Barber) writes: >Perhaps I am wrong, but my understanding of headers (from the RFC 822 >point of view, at least), is that they form the envelope of the message >and the "To:" line is for the benefit of the mailer as well >as the recipient. The uux command line is generated from data contained in >the header (on my systems, at least). That doesn't contradict what has been suggested. Just because the originating system generates the delivery instructions (the "uux" command line), but the receiver merely uses the uux parameters. This is, in effect, the envelope. The Header is not equivalent to the envelope. In your example, the Unix mailer is generating the envelope from the header (as a secretary might do if you gave her a letter and asked her to put it in an envelope and mail it). >I also think that it is a bit naive to assume that any site will >just forward a message without "looking" at it. This implies that >systems will look at the "To:" line before forwarding. In UUCP it is necessary for sites to look at and modify headers as they pass through, because UUCP paths have to be rewritten. This is not true in the Arpa Internet, because host names are global. In environments where SMTP (or CCITT's X.400 protocols) are used for mail transfer, the receiving system does not need to look at the message at all. The recipient of a message is specified in SMTP with the "RCPT TO:" command. The following is well within the SMTP (RFC 821, I believe) protocol: MAIL FROM:<Sender1@HOST1> RCPT TO:<UserA@HOST2> DATA From: <Sender2@HOST3> To: <UserB@Host3> This is a message being delivered to someone who is not in the header. . This might occur because UserB is a blind-copy recipient. The right way to think about this is by analogy with paper mail. The envelope is the delivery instructions, analogous to the stuff you write on the paper envelope (recipient's mailing address and sender's return address). The header corresponds to the inside address. I'm sure most of you have received mail at work which had your name on the envelope, but which contained a letter that started with To: All Employees In general, the envelope is information for the delivery agents, while the header is information from the sender to the recipient. In the real world, the post office uses the return address when returning undeliverable mail, while the recipient replies to the person named in the letter. -- Barry Margolin ARPA: barmar@MIT-Multics UUCP: ..!genrad!mit-eddie!barmar
eric@grkermi.UUCP (Eric N. Starkman) (08/22/85)
In article <5063@mit-eddie.UUCP> barmar@mit-eddie.UUCP (Barry Margolin) writes: > The recipient of a message is specified in SMTP with the "RCPT >TO:" command. The following is well within the SMTP (RFC 821, I >believe) protocol: > >MAIL FROM:<Sender1@HOST1> >RCPT TO:<UserA@HOST2> >DATA >From: <Sender2@HOST3> >To: <UserB@Host3> >This is a message being delivered to someone >who is not in the header. >. > >This might occur because UserB is a blind-copy recipient. ^^^^^ should read UserA. The rcpt to:<> has UserA in it, and that's where the message will go. > Barry Margolin > ARPA: barmar@MIT-Multics > UUCP: ..!genrad!mit-eddie!barmar -Eric Starkman ARPA: starkman@mit-athena UUCP: ...decvax!genrad!panda!ens
honey@down.FUN (Peter Honeyman) (08/23/85)
I take issue with Barry's assertion: In UUCP it is necessary for sites to look at and modify headers as they pass through, because UUCP paths have to be rewritten. This is not true in the Arpa Internet, because host names are global. UUCP never looks at the data file (except to transfer it). And in standard UNIX, rmail prepends a "From user <date> remote from host" line, but otherwise leaves the message untouched, headers (which are not distinguished from the body) and all. Perhaps Barry refers to Berkeley UNIX, which is hardly a guide for proper mail handling. peter