Many mail clients on personal computers are now using a non- standard "X-Sender" header to identify the originator of a message without the implication that the sender has a known deliverable mailbox (unlike the "Sender" header). Usually this "X-Sender" header is constructed from the credentials used to login to a POP [POP3], IMAP [IMAP4], or NNTP [NNTP] server. Such credentials often do not refer to a deliverable mailbox, and therefore MUST NOT be used to construct a return or reply address.

I disagree strongly with your contention that all headers are equally untrustable. *Untrustworthy* they may be, and always in need of better authentication (a whole new protocol built around RFC 1113 encapsulation, perhaps?), but there is an implicit trust placed in the standard headers that you can't possibly deny. To say that the To: header "[has] no value" is a bit silly for a vendor of an SMTP relay. And my statement about "x-" is completely correct: it "signifies" an untrustworthy header BECAUSE the "x-" headers are unstandardized, hence not to be processed by RFC-compliant relays, whereas the standard headers, despite your objection, are to be taken as relatively trustworthy and used to deliver mail. X-sender: seems to me to be a comment on the essential untrustworthiness of Sender:, but that doesn't change the fact that whatever ends up in the Sender: position is trusted (in the absence of a From:, right?).

Regards,

Sandy

> -----Original Message----- > From: IMail_Forum-owner@list.ipswitch.com > [mailto:IMail_Forum-owner@list.ipswitch.com]On Behalf Of Len Conrad > Sent: Wednesday, October 25, 2000 3:05 PM > To: IMail_Forum@list.ipswitch.com > Subject: RE: [IMail Forum] HEADER QUESTION > > > > >Thing is, the "x-" in x-sender signifies an untrustworthy > header, so you're > >sort of working against yourself... > > x means experimental, if, not an Internet standard. > > All headers are untrustable, and so have no value as identification > or authentification. > > Len > > > http://BIND8NT.MEIway.com: ISC BIND 8.2.2 p5 & 8.2.3 T6B for NT4 & W2K > http://IMGate.MEIway.com: Build free, hi-perf, anti-spam > mail gateways > > > > > >