* Ken Reiss (kreiss@???) [990413 19:00]:
> I have exim set to allow up to 50 concurrent connections. During a time
> when my relay machine was receiving mail, I did a netstat on the primary
> and saw only 10 connections.
>
> My question is why/how does an outside sender decide to go to my relay
> machine, when my main machine is not refusing connections?
A couple of ideas:
1. The decison to try the next MX host in a list is based upon the initial
connection timeout at the other end. You're obviously not in control of
that value, so if the remote end has it set to a low value and latency
between the two sites is high, the other system might timeout on your
primary MX and go to the secondary MX. Sendmail has an option to set the
timeout on the first connection attempt to a different value than subsequent
attempts. The idea is to deliver mail to well-connected hosts quicker than
to poorly-connected hosts. You may be falling victim to this algorithm.
2. If you are using Exim options like 'helo_verify' on the primary host but
not on the secondary host, you may find that hosts with mismatched reverse
DNS are connecting to your first MX host, being refused, then attempting
your secondary MX host and getting through.
--
j.
James FitzGibbon (JF647) james@???
EHLO Solutions Voice/Fax (416)410-0100
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