[Mailman-Users] Non-Delivery of Mail

Mark Sapiro mark at msapiro.net
Sat Jan 28 14:00:33 EST 2017

On 01/28/2017 10:26 AM, David Andrews wrote:
> When I look at a mail delivery report via cPanel, I see messages that
> say 421 too many concurrent connections, connection refused.  What can I
> change to fix this problem!

That's a retryable error and may or may not eventually be successfully
retried depending on what's actually causing it.

The recipient MX is saying your IP already has the maximum number of
concurrent connections open and it won't accept this additional one.

The connections in question are presumably those from Exim on the cPanel
host to the recipient MX since Mailman will never open more concurrent
delivery SMTP sessions to Exim than there are OutgoingRunner slices
(default 1).

You might be able to tell from the Exim logs how many other deliveries
to that MX have been started and not completed when the error occurs.

I'm not an Exim expert by any means, but it looks like Exim's
queue_run_max setting might affect this. The default is 5 which should
be small enough, but if you have it set to a large number or to 0 ->
unlimited, this could be the issue.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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