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[fetchmail]Re: fetchmail problem with SMTP forwarding and sendmail's "delay_checks" feature.

2001-07-06 01:44:35
I've taken the liberty of copying this reply to fetchmail-friends in order
to invite comment from the experts there.

Paul Howarth <paul(_at_)city-fan(_dot_)org>:
I've been using fetchmail for many years now without problems (thanks!).
Recently I was fiddling with my sendmail configuration and I decided to
implement FEATURE(delay_checks, friend), so that I could accept mail to
postmaster from sites otherwise blocked by my access database.

The effect of this feature is that the MAIL FROM: address is always
accepted OK, and any rejection of the sender is delayed until the
RCPT TO: part of the SMTP transaction. This includes rejects such as
553 for invalid sender address.

Since making this change, I've found that fetchmail cannot deliver mail
with invalid sender addresses, so I get lots of bounce messages when some
spammers hit my mailbox (a pair of bounces every time fetchmail runs; one
to FETCHMAIL-DAEMON generated by sendmail when fetchmail's bounce to the
spammer is rejected, and one postmaster notify for that bounce). I think
(but I'm not sure) that fetchmail only recognises the 553 response in
reply to MAIL FROM: and not RCPT TO:; is that right?

For the moment I have worked around this problem by getting fetchmail to
deliver using procmail as an MDA rather than forwarding via sendmail. Is
my diagnosis right?

I think so, and actually I'm quite grateful to you.  I think you've just
succeeded in clarifying an issue that has been really murky for a while.

If you look near sink.c:690 you'll find conditioned-out code that was
an attempt to deal with exactly this problem of invalid RCPT TO
addresses.  The comment explains why it didn't work.  I'm now thinking
that the right fix may be to reinstate that code but stop
handle_smtp_report from implicitly calling RSET.
-- 
                <a href="http://www.tuxedo.org/~esr/";>Eric S. Raymond</a>

In recent years it has been suggested that the Second Amendment
protects the "collective" right of states to maintain militias, while
it does not protect the right of "the people" to keep and bear arms.
If anyone entertained this notion in the period during which the
Constitution and the Bill of Rights were debated and ratified, it
remains one of the most closely guarded secrets of the eighteenth
century, for no known writing surviving from the period between 1787
and 1791 states such a thesis.
        -- Stephen P. Halbrook, "That Every Man Be Armed", 1984


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