On 10/3/2023 2:11 PM, Kevin C via Postfix-users wrote:
Hi Matthew, Hi Wietse,
Our postfix servers are only MTAs who transfer mails from internal IT apps to
end users over Internet. We don't receive mails from Internet.
Sometimes, an abnormal activity can fill active queue unitl it's full, and it
slow down all mail delivery. We had some rules to slow down delivery to
specif destination, some other to send mail more quickly for others, and
remains with default smtp delivery configuration.
As a general rule, you want postfix to deliver as fast as possible.
This may be limited by what the receiving system is willing to
accept. For high volume to really slow destinations, it might be
beneficial to setup another "slow" postfix box as a relay to keep
the main queue moving quickly.
If you're using some kind of content filter, quite likely that's
what is slowing things down. Work on getting the filter to process
faster. Maybe you need more (or fewer!) processes, more memory,
faster disks, or offload to more machines. You'll need to analyze to
find the bottleneck.
I was wondering if we can rate limit connections to Postfix to reject mails if
active queue are full (I know postfix can accept mail to incoming queue when
active queue is full), when a client send a unusual number of messages.
http://www.postfix.org/TUNING_README.html
http://www.postfix.org/STRESS_README.html
http://www.postfix.org/QSHAPE_README.html
My first wild guess is setting in_flow_delay to a higher value might
help. Note this may be completely inappropriate for your specific
application.
http://www.postfix.org/postconf.5.html#in_flow_delay
There are also various limits described in
http://www.postfix.org/TUNING_README.html#conn_limit
Note these limits are intended to limit attacks and not to regulate
legit traffic, as any host slowed by these limits will likely see
significant delays. But maybe that's what you need.
-- Noel Jones
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