GMX (www.gmx.net), a large email provider in the German language areas
of Europe (.de/.at/.ch/.li), seems to have implemented some form of
homegrown return path rewriting. They currently rewrite the envelope
sender on forwarded mail to something like:
bounce=XXX#aYYY.ZZ=TS=COOKIE=USER@gmx.{net,de,at,ch,li}
where XXX@YYY.ZZ was the original return path, and USER@gmx.net is the
forwarding mail account, TS is a timestamp ('28' for valid until the
28th of the month, probably; they seem to use a validity period of 4
days), and cookie is a 2 byte cookie (4 lower case hex digits). Note
that they substitute '@' with '#a'.
No guarantees about the correctness -- this analysis of their scheme is
just based on some days worth of MTA logs.
GMX also has had their homegrown static envelope sender filters for
quite some time (only accept @yahoo.com from Yahoo's outbound MTAs,
etc), so it seems like a natural step that they'd also want to conform
to the same kind of rules they enforce on incoming mail.
Cheers,
Dan
--
Daniel Roethlisberger <daniel@roe.ch>
GnuPG key ID 0x804A06B1 (DSA/ElGamal)
of Europe (.de/.at/.ch/.li), seems to have implemented some form of
homegrown return path rewriting. They currently rewrite the envelope
sender on forwarded mail to something like:
bounce=XXX#aYYY.ZZ=TS=COOKIE=USER@gmx.{net,de,at,ch,li}
where XXX@YYY.ZZ was the original return path, and USER@gmx.net is the
forwarding mail account, TS is a timestamp ('28' for valid until the
28th of the month, probably; they seem to use a validity period of 4
days), and cookie is a 2 byte cookie (4 lower case hex digits). Note
that they substitute '@' with '#a'.
No guarantees about the correctness -- this analysis of their scheme is
just based on some days worth of MTA logs.
GMX also has had their homegrown static envelope sender filters for
quite some time (only accept @yahoo.com from Yahoo's outbound MTAs,
etc), so it seems like a natural step that they'd also want to conform
to the same kind of rules they enforce on incoming mail.
Cheers,
Dan
--
Daniel Roethlisberger <daniel@roe.ch>
GnuPG key ID 0x804A06B1 (DSA/ElGamal)