Looking for advice... I have a Postfix mail server on a relatively slow 1.5Mbit/s dedicated link. (It used to be relatively fast. Now it is relatively slow.) It receives a lot of mailing list email from a well connected mailing list server running Exim.
Periodically a large wave of email from the mailing lists will be unleashed. Such as when upstream connectivity is down for a while causing a backlog and then it is restored causing a transfer of the backlog. Then the upstream Exim mail server decides to open 36 concurrent client connections. Server resources are not any problem. But network bandwidth resources are limited. Each will split the network bandwidth and get 2.7% or less of the bandwidth. Of course eventually the mail is transferred. The problem is that any *other* network connection is also competing with those and each get a split of the bandwidth. Everything else suffers. Even interactive ssh connections are tedious to use. On first guess I would like to limit the number of concurrent clients. I look and see smtpd_client_connection_count_limit=50 and immediately think I should reduce that number to something smaller, say less than 10 as a start. But it also includes this stern warning. WARNING: The purpose of this feature is to limit abuse. It must not be used to regulate legitimate mail traffic. But there isn't any rationale on why not. Also it doesn't give any hints as to suggestions to limit the number of incoming clients if that isn't to be used. Since this email from the upstream mailing list server is legitimate. And so here I am querying the wisdom of the net to see why using smtpd_client_connection_count_limit would be bad and what alternative strategies exist. Thanks, Bob
