[pfx] Re: Trying to limit the number of users per connection and the number of concurrent connections to one domain

[Paul Tomblin via Postfix-users]

On Fri, Jun 26, 2026, at 3:43 PM, Wietse Venema via Postfix-users wrote:
>
> - Check any parameter settings in master.cf
>
>     postconf -P | grep slow_smtp

# postconf -P |grep slow_smtp
slow_smtp/unix/syslog_name = postfix-slow


>
> - Be sure to execute "postfix reload" after changing scheduler
> settings. Unlike most Postfix programs, the qmgr does not autoimatically
> refresh.

I do that every time. Sometimes I do a systemctl restart just to make sure.

>
> - Provide proof that the slow_smtp transport is handling those
> messages. 

In /var/log/mail.log, messages to that domain, and only to that domain, have 
the "postfix-slow" prefix as specified in master.cf.
2026-06-26T17:58:26.784276+00:00 mail postfix-slow/smtp[1046598]: 89A2C82E43: 
to=<cbenzi...@rochester.rr.com>, 
relay=pkvw-mx.msg.pkvw.co.charter.net[47.43.26.7]
:25, delay=1.2, delays=0.3/0.05/0.35/0.52, dsn=2.0.0, status=sent (250 2.0.0 
dAorwNQVCzLiadAoswI9Zm mail accepted for delivery)
2026-06-26T17:58:26.784455+00:00 mail postfix-slow/smtp[1046598]: 89A2C82E43: 
to=<cdelv...@rochester.rr.com>, 
relay=pkvw-mx.msg.pkvw.co.charter.net[47.43.26.7]:
25, delay=1.2, delays=0.3/0.05/0.35/0.52, dsn=2.0.0, status=sent (250 2.0.0 
dAorwNQVCzLiadAoswI9Zm mail accepted for delivery)
2026-06-26T17:58:26.784528+00:00 mail postfix-slow/smtp[1046598]: 89A2C82E43: 
to=<cra...@rochester.rr.com>, 
relay=pkvw-mx.msg.pkvw.co.charter.net[47.43.26.7]:25
, delay=1.2, delays=0.3/0.05/0.35/0.52, dsn=2.0.0, status=sent (250 2.0.0 
dAorwNQVCzLiadAoswI9Zm mail accepted for delivery)
...
2026-06-26T17:58:29.437907+00:00 mail postfix/smtp[1046596]: 89A2C82E43: 
to=<al...@allenhopkins.org>, relay=freerelay.err.no[178.255.151.162]:2525, 
delay=3.9, delays=0.3/0.04/1.2/2.3, dsn=2.0.0, status=sent (250 OK 
id=1wdAou-00000005xEn-2SDu)
2026-06-26T17:58:29.438110+00:00 mail postfix/smtp[1046596]: 89A2C82E43: 
to=<ahah...@aol.com>, relay=freerelay.err.no[178.255.151.162]:2525, delay=3.9, 
delays=0.3/0.04/1.2/2.3, dsn=2.0.0, status=sent (250 OK 
id=1wdAou-00000005xEn-2SDu)
2026-06-26T17:58:29.438198+00:00 mail postfix/smtp[1046596]: 89A2C82E43: 
to=<bexh...@aol.com>, relay=freerelay.err.no[178.255.151.162]:2525, delay=3.9, 
delays=0.3/0.04/1.2/2.3, dsn=2.0.0, status=sent (250 OK 
id=1wdAou-00000005xEn-2SDu)
2026-06-26T17:58:29.438264+00:00 mail postfix/smtp[1046596]: 89A2C82E43: 
to=<boscobe...@aol.com>, relay=freerelay.err.no[178.255.151.162]:2525, 
delay=3.9, delays=0.3/0.04/1.2/2.3, dsn=2.0.0, status=sent (250 OK 
id=1wdAou-00000005xEn-2SDu)

>
> The _destination_concurrency_limit and _smtp_destination_recipient_limit
> features are implemented by decades-old code that has not changed
> $forever.

I'm still operating under the default assumption that it's something I'm doing 
wrong, not something postfix is doing wrong.

-- 
Paul Tomblin
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