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Re: [ietf-smtp] You can't hurt a computer's feelings

2013-03-04 03:24:35
On 4/3/2013, at 1:14 ᴘᴍ, Randall Gellens 
<randy(_at_)qti(_dot_)qualcomm(_dot_)com> wrote:

At 11:22 AM -0500 3/3/13, John R Levine wrote:

That matches my experience.  Whatever problem might once have been addressed 
by limiting the number of connections per source, it doesn't exist any more.

I misstated the EIMS restrictions in my original message.  When I checked the 
documentation, it turns out that EIMS does not enforce restrictions on number 
of connections from the same source.  Instead, EIMS has a three-level budget: 
total number of incoming connections; number reserved for hosts in the OK 
state (having passed graylisting); and number reserved for whitelisted hosts. 
 I apologize for mischaracterizing the restrictions (I blame faulty 
recollection and being too lazy to check before writing).

EIMS also has restrictions on the number of connections from the same IP, it is 
an older setting that I didn't remove when I added the newer priority based 
limits, it can still be handy for blocking some trivial DoS attacks.

I agree that a limit per IP is pretty much irrelevant if a bot-net is trying to 
send you spam, and that is definitely a far more common problem these days. On 
a number of occasions I've seen more than 60,000 unique IPs over 24 hours 
repeatedly trying to connect to one of my servers that would normally handle 
~100 legitimate messages a day. Reserving some connections for recently seen 
well behaved hosts and for whitelisted hosts definitely helps legitimate mail 
to get through under those circumstances.


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