In <1102058379(_dot_)28489(_dot_)76(_dot_)camel(_at_)alakazee> Andy Bakun
<spf(_at_)leave-it-to-grace(_dot_)com> writes:
Sorry for the length... I know few people read my messages anyway, being
the thread killer that I am. ;)
I found youre message, although long, quite informative. Thanks.
Why did we stop exploring reverse source routing as a "solution" to
forwarding?
Mostly because the language in RFC2821 basically says that source
routes SHOULD NOT be created and the routing they imply SHOULD be
ignored. So, the use of source routes instead of SRS-like encoding is
in violation of RFC2821. It's use will be unreliable, at best.
Section 3.3 "Mail Transactions" says that:
Historically, the <forward-path> can be a source routing list of
hosts and the destination mailbox, however, contemporary SMTP clients
SHOULD NOT utilize source routes (see appendix C). Servers MUST be
prepared to encounter a list of source routes in the forward path,
but SHOULD ignore the routes or MAY decline to support the relaying
they imply. Similarly, servers MAY decline to accept mail that is
destined for other hosts or systems. [...]
Section 3.7 "Relaying" says that:
In general, the availability of Mail eXchanger records in the domain
name system [22, 27] makes the use of explicit source routes in the
Internet mail system unnecessary. Many historical problems with
their interpretation have made their use undesirable. SMTP clients
SHOULD NOT generate explicit source routes except under unusual
circumstances. SMTP servers MAY decline to act as mail relays or to
accept addresses that specify source routes. When route information
is encountered, SMTP servers are also permitted to ignore the route
information and simply send to the final destination specified as the
last element in the route and SHOULD do so.
Section 4.1.1.3 "RECIPIENT (RCPT)"
[...] Sending systems SHOULD not generate the optional list of
hosts known as a source route. Receiving systems MUST recognize
source route syntax but SHOULD strip off the source route
specification and utilize the domain name associated with the mailbox
as if the source route had not been provided.
Similarly, relay hosts SHOULD strip or ignore source routes, and
names MUST NOT be copied into the reverse-path. [...]
-wayne