On Thu, Sep 24, 2020 at 12:59:44AM -0600, Bob Proulx wrote:
> Question about a different system. Pretty much every question of mine
> is related to a different oddball case. Here I am helping a friend
> out and they encountered this problem. I'll change the 3rd party
> addresses so as not to annoy them but the data is otherwise
> verbatim.
>
> Sep 23 14:38:23 yuki postfix/smtp[21081]: CDC7E1438D:
> to=<us...@comcast.net>, relay=mx2.comcast.net[68.87.20.5]:25, delay=2.7,
> delays=0.08/0.06/2.5/0.05, dsn=4.1.0, status=deferred (host
> mx2.comcast.net[68.87.20.5] said: 421 4.1.0 104.200.24.137 Throttled - try
> again later. Please see
> http://postmaster.comcast.net/smtp-error-codes.php#RL000001 (in reply to MAIL
> FROM command))
> Sep 23 14:38:23 yuki postfix/smtp[21081]: CDC7E1438D:
> to=<us...@comcast.net>, relay=mx2.comcast.net[68.87.20.5]:25, delay=2.7,
> delays=0.08/0.06/2.5/0.05, dsn=4.1.0, status=deferred (host
> mx2.comcast.net[68.87.20.5] said: 421 4.1.0 104.200.24.137 Throttled - try
> again later. Please see
> http://postmaster.comcast.net/smtp-error-codes.php#RL000001 (in reply to MAIL
> FROM command))
> Sep 23 14:38:23 yuki postfix/smtp[21081]: CDC7E1438D:
> to=<us...@comcast.net>, relay=mx2.comcast.net[68.87.20.5]:25, delay=2.7,
> delays=0.08/0.06/2.5/0.05, dsn=4.1.0, status=deferred (host
> mx2.comcast.net[68.87.20.5] said: 421 4.1.0 104.200.24.137 Throttled - try
> again later. Please see
> http://postmaster.comcast.net/smtp-error-codes.php#RL000001 (in reply to MAIL
> FROM command))
Look carefully at the log entry. The "421" is send in response to "MAIL
FROM", not "RCPT TO". So the recipient limit does not look entirely
plausible. A good test would be to disable "pipelining" in a custom
smtp(8) transport, and use that for Comcast. That would definitely
rule out recipient count limits if the reject is still at "MAIL FROM".
Furthermore, looking at (the reject did say "Please see ..."
http://postmaster.comcast.net/smtp-error-codes.php#RL000001
suggests a reputation issue and rate limits based on that. I don't see
anything about recipient concurrency.
> It seems that the way to add limits when sending to Comcast would be
> to set up a transport map such as perhaps this. (And knowing that
> Yerdle is a turtle.)
Since that's not demonstrated (or very likely) to be the problem,
changing the recipient limits is NOT a good idea.
> smtp unix - - - - - smtp
> yerdle unix - - - - - smtp
>
> And add this to the main.cf file.
>
> yerdle_destination_concurrency_limit = 1
> yerdle_destination_rate_delay = 1s
> yerdle_destination_recipient_limit = 1
A recipient limit of 1 is "magic" and will not do what you want,
instead, it will drive up delivery concurrency, making the
problem likely worse.
> That it would allow one connection at a time, with one recipient per
> message at a time, and then a small delay between sending of messages.
The problem is the IP reputation...
--
Viktor.
