[exim-dev] [Bug 1788] Deliveries to one ISP sometimes fail s…

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Vastaanottaja: exim-dev
Aihe: [exim-dev] [Bug 1788] Deliveries to one ISP sometimes fail silently after T=remote_smtp defer on first delivery attempt
https://bugs.exim.org/show_bug.cgi?id=1788

--- Comment #1 from Alex Presland <exim@???> ---
I've got log examples where emails to these email addresses have been deferred
one or more times and then delivered successfully.

Correction: Emails to @waitrose.com have all been successfully re-delivered.

The path of the mail going through the server is "a little complicated" in the
cases that the emails silently fail to retry. This path is:

[1] Email presented to server for delivery to first.last@???
[2] The domain1.org.uk alias file sends the email to the 'spamcatcher' user
account. This account's purpose is to stop spam from being relayed by the
server, and thus protect its reputation.
[3] The 'spamcatcher' user account applies a load of Exim Filter commands via
its .foward file. If the email isn't quarantined / discarded, it is delivered
to "filtered-$original_local_part@$original_domain". Thus, it is presented
back to the domain1.org.uk alias file.
[4] The alias file for domain1.org.uk translates
filtered-first.last@??? to the real email address
user@??? for delivery.

>From what I've can see, all deliveries work fine if successful on the first

attempt, but if they get the "R=dnslookup T=remote_smtp defer (-53): retry time
not reached for any host" from the first delivery attempt then they won't try
again.

I've also found an example that does two alias file translations in [4], which
shows that if the first defer was a "R=dnslookup T=remote_smtp defer (0): SMTP
error from remote mail server after initial connection: host mx.avasin.plus.net
[212.159.8.200]: 421 avasin09.plus.net Plusnet Cloudmark Gateway Too many
connections from same IP" and the second defer was a "R=dnslookup T=remote_smtp
defer (-53): retry time not reached for any host", then the email was delivered
correctly on the third attempt.

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