[exim] Rate limiting connections

I am implementing connection rate limiting connections from site-local hosts, some of which have anti-social behavior and use up all of the available IP connection sockets at times. Currently I have inherited a setting of



smtp_connect_backlog = 40


# max number of concurrent SMTP connections


smtp_accept_max = 60


# don't attempt immediate delivery when more than 40 connections

# in progress (default = 10)


smtp_accept_queue = 40

In respect of smtp_accept_max is there some upper limit and, for RH Linux, how do I find out what this may be. There is presumably some Kernel limit, but there are other things to consider too. Is this just something people adjust hubristically or is there a more scientific approach?

Same question for smtp_connect_backlog.

Do not assume what I have inherited makes any sense.

Best

Rob

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