To: Dave Crocker <dcrocker(_at_)mordor(_dot_)stanford(_dot_)edu> (Non Receipt
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Cc: David Herron <david(_at_)twg(_dot_)com> (Non Receipt Notification
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ietf-822(_at_)dimacs(_dot_)rutgers(_dot_)edu (Non Receipt Notification
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Since you're the second person to mention these on the mailing list recently.
These all come from RFC-1148 (and there's a newer version whose number
escapes me at the moment). They are X.400's P1 and P2 options encoded into
an RFC-822 header. They are the only `standard' for doing these kinds
of things in Internet mail.
David
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