Generally speaking when I advise senders on their rate limits, I have them use
the smallest denominator possible, because most commercial MTAs will take a
per-hour rate limit and implement it as "send the hour's allotment in a single
burst and then wait 59 minutes", which I don't think most receivers want, so I
advise setting a per second limit when possible. One message per second is
better than 3600 messages per hour if it means a 3600 message burst and then a
long wait.
Mike
-----Original Message-----
From: ietf-smtp <ietf-smtp-bounces(_at_)ietf(_dot_)org> On Behalf Of Ned Freed
Sent: Monday, April 19, 2021 7:34 PM
To: John R Levine <johnl(_at_)taugh(_dot_)com>
Cc: Ned Freed <ned(_dot_)freed(_at_)mrochek(_dot_)com>;
ietf-smtp(_at_)ietf(_dot_)org
Subject: Re: [ietf-smtp] [Emailcore] Proposed ESMTP keyword RCPTLIMIT
On Mon, 19 Apr 2021, Ned Freed wrote:
I'm especially interested in people's thoughts on rate limits. The
problem I have with rate limits is, well, how to express them. ...
A little surveying might be in order.
I see that Postfix lets you set both the numerator and denominator of
the rate limit, but the denominator defaults to a minute. It has
separate rate limits for connections and messages.
Exim also lets you set both, the examples use an hour. The
documentation says that if you use a large interval that lets people send
bursts.
Sounds familiar. Oracle Messaging Server lets you set both; the denominator
default is one hour.
We store the limits in memcache or Redis so they can apply across mutiple MTAs.
The usual limit is per-IP, but we support per-host and per-domain as well.
The demoninator in PowerMTA is a string rather than a number, possible values
are sec, s, min, m, hr, or h. It supports per-IP and per-host and probably
other stuff; my familiarity here is limited.
I assume the Exim and Postfix limits are per-host, which in most cases
translates to per-IP.
I have to say there's more consistency here than I expected.
Ned
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