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Re: [ietf-smtp] parsing SMTP replies

2021-03-19 07:15:30

We (MessageSystems/SparkPost, makers of the Momentum and PowerMTA mtas)
already support interpreting smtp responses to infer requested behavior in
regards to the number of connections and message velocity limits. As Laura
notes, this is already established behavior with some large providers.
Today we have to parse the whole response string to comply with different
providers bespoke strings. A set of extended codes to make this
standardized and easier to parse would be fantastic.


On Fri, Mar 19, 2021 at 04:55 Laura Atkins <laura(_at_)wordtothewise(_dot_)com> 

On 18 Mar 2021, at 23:27, Jeremy Harris <jgh(_at_)wizmail(_dot_)org> wrote:

On 18/03/2021 23:15, Michael Peddemors wrote:

If you show me MTA's currently advertising limits on how much they accept,
then it may be something that needs to be addressed.

Apart from people building prototypes to demo this proposal, there are no
such MTAs precisely because there is no standard to do so.

The MTAs aren’t advertising limits, but the companies running the MTAs do
set limits on senders. There’s just no programatic way to advertise them.

Yahoo: limits connections, also limits the number of emails per connection
and will just close connections after that limit has been reached.

Gmail: prefers fewer connections and as much mail shoved through it as

Microsoft: admits there is a limit to connections, but does not make that

Modern bulk MTAs have built in controls so these limits can be manually
configured. They also have AI / ML / automatic processes that will modify
sending behavior on the fly. These can be per MX, IP, MX cluster, or

These things are happening already (and have been for a decade) they’re
just not standardized.


Either way, it seems like the wrong time/place to put in standards for a
need that is not yet apparent.

The need is for a more efficient, in roundtrips, way of communicating
than getting individual command responses.

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