On 08 June 2002, Juha Saarinen said:
> Could someone enlighten me as to what happens if mail forwarding is set up
> like this:
>
> Sender -> Forwarding domain -> Final recipient domain
>
> What I'm curious about is if the SMTP conversation goes something like
> this:
>
> HELO "Forwarding domain"
> MAIL FROM:<Sender>
> RCPT TO:<"Someone@FinalRecipient.Domain">
>
> I think it does...? Do some MTAs do it differently, using something else
> in MAIL FROM:<> than $Sender?
They should not do so. Eg. I'm 99% certain that in my case (my public
address is gward@python.net, which forwards to gward@my.isp -- and no
I'm not posting the real address), then the first connection -- random
host to python.net -- goes like
EHLO host.random.domain
MAIL FROM:<joe@random.domain>
RCPT TO:<gward@python.net>
(NB. HELO expects a hostname not a domain name.)
When qmail on python.net's MTA finds gward@my.isp in my ~/.qmail file,
it connects to my.isp and does
EHLO starship.python.net
MAIL FROM:<joe@random.domain>
RCPT TO:<gward@my.isp>
IOW, the envelope sender should be preserved through the chain of
forwards. But then, qmail is a sane MTA, so of course it does the right
thing. I'm sure postfix, Exim, and sendmail also do the right thing.
AFAICs, the only time it's legitimate to change the envelope sender is
when you go through a mailing list -- eg. the MLM managing this list
will process this message so it winds up in your inbox with envelope
sender "exim-users-admin@exim.org". That way only one agent (the MLM,
and maybe the human behind it) has to worry about bouncing list mail,
rather than each individual poster being bothered by bounces.
Greg
--
Greg Ward - software developer gward@mems-exchange.org
MEMS Exchange
http://www.mems-exchange.org