North American Network Operators Group

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Re: Time to check the rate limits on your mail servers

  • From: Sam Hayes Merritt, III
  • Date: Fri Feb 04 11:50:13 2005

On Thu, 3 Feb 2005, Michael Loftis wrote:
--On Thursday, February 03, 2005 11:42 +0000 [email protected] wrote:

Do you let your customers send an unlimited number of
emails per day? Per hour? Per minute? If so, then why?
Because there are *NO* packages available that offer limiting. Free or commercial.
I disagree.

On a per IP basis, sendmail now offers

ClientRate, number of connections allowed within a 60 second sliding window from a given IP


ClientConn, number of active connections allowed from an IP at any time

Used in conjunction with Jochen Bern's bm patch available from which limits the number of mail commands given in a single connection, you can rate limit your users fairly well. We have used these limits for ~6 months now and have only had to whitelist 3 sites from the Client limits.

You could probably adjust the window size for the ClientRate and then limit the number of smtp commands per connection to achieve like an hourly limit of some sort.