Re: [ietf-smtp] [Emailcore] Proposed ESMTP keyword RCPTLIMIT

Ned Freed <ned.freed@mrochek.com> Tue, 20 April 2021 14:50 UTC

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Cc: Ned Freed <ned.freed@mrochek.com>, John R Levine <johnl@taugh.com>, "ietf-smtp@ietf.org" <ietf-smtp@ietf.org>
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Date: Tue, 20 Apr 2021 07:44:32 -0700 (PDT)
From: Ned Freed <ned.freed@mrochek.com>
In-reply-to: "Your message dated Tue, 20 Apr 2021 12:24:00 +0000" <BN6PR22MB022669CD015B89D47AA063F3DA489@BN6PR22MB0226.namprd22.prod.outlook.com>
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To: Mike Hillyer <mike@mikehillyer.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf-smtp/XKDliNn10-JZvqYy7xqjE0RMH_Y>
Subject: Re: [ietf-smtp] [Emailcore] Proposed ESMTP keyword RCPTLIMIT
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Interesting and good to know. Thanks.

				Ned

> 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@ietf.org> On Behalf Of Ned Freed
> Sent: Monday, April 19, 2021 7:34 PM
> To: John R Levine <johnl@taugh.com>
> Cc: Ned Freed <ned.freed@mrochek.com>om>; ietf-smtp@ietf.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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