Re: sendmail gateway overrunning my internal mailhost

On 2005-08-13, Fred Oo <foo@xxxxxxxxxx> wrote:
> My external mail gateway (sendmail 8.11.6) is over running my
> internal SMTP and POP hosts. The sendmail server is opening connections
> faster than the internal one can handle the requests. As the internal
> machine slows, it takes longer to respond, sendmail opens another connection
> and the cycle continutes. Is there a sendmail option to limit the number of
> outbound connections sendmail will make. I think I would be better off,
> having my mqueue grow during peaks and then drain, rather than having all
> the connections hit my internal sever real time.

(Please upgrade to Sendmail 8.12.10 or better; 8.11.6 has several
security problems.)

The general recipe is to set DeliveryMode to "queue", and limit the
number of concurrent queue runners, either through MaxQueueChildren or
via queue group definitions. The devil is in the details though; some
questions first:

* Does your gateway accept recipients regardless of whether they exist
on the internal host? Nowadays spammers undertake massive dictionary
attacks looking for valid addresses. Rejecting these attempts at the
perimeter cuts down on a *lot* of traffic.

* Are the internal hosts under your control, and if so, what software
are they running? Restricting the number of connections on the
incoming side is both simpler and more efficient, especially if you
have more than one gateway host.

* Does the gateway handle both incoming and outgoing traffic?

* Are separate limits needed for each host/group of hosts?
.

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