Hello list,
I run a centos 4.4 final server using qmail-toaster-1.03-1.3.5 from a
few months ago. Recently, in the past couple months, I've had
intermittent issues where my server becomes unresponsive for a few
minutes at a time, several times a day. Unresponsive to the web
server it runs, dns queries, mail, ssh etc. I tracked down the
problem to random IP addresses opening a bunch of smtp processes and
attempting to send spam to my server.
I run a four domains and a few e-mail users of a personal nature.
Nothing mission critical here. However, it is annoying the server
gets pretty much tied up dealing with the spam.
I checked my server to make sure it isn't an open relay, which came
back clean. I have no auto-responders, nor any catch alls.
I edited /var/qmail/control/concurrencyincoming to 50 instead of the
100 and that made no difference.
The server is a P4 2.4ghz, with 512mb of ram, couple of drives in a
Raid1 configuration, on a shared T1 line. I don't use much bandwidth,
however the bandwidth is there if I need it. So I do not think this
is an issue with internet connectivity. I can always ping the server
remotely and all responses come back properly.
I checked the smtp logs, and see random IP addresses trying to send
mail to my server. No one IP address repeatedly trying to connect, so
blocking IP addresses was a futile effort. I do use the blacklists
and that helps somewhat. I also have spamassassin installed which
helps a bit with the spam e-mails.
Most of the spam e-mails are directed to non-existent e-mail accounts.
Is there anything I can do to limit the amount of connections one ip
address is allowed to open at one time? Or something else I can do to
not make my server so unresponsive?
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