Re: [ietf-smtp] SMTP, DSNs, and enhanced replies (was: Re: SMTP server reply extensions)

Hector Santos <> Thu, 09 April 2020 14:17 UTC

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Date: Thu, 09 Apr 2020 10:17:08 -0400
From: Hector Santos <>
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Subject: Re: [ietf-smtp] SMTP, DSNs, and enhanced replies (was: Re: SMTP server reply extensions)
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Hello John. I hope all is well during this crisis.

I support a technical summary of OPTIONAL Extended Reply Codes (ERC), 
include some examples but definitely provide references related to ERC.

While ERC is widely supported, not every SMTP system needs them and do 
not implement them. The key consideration is that ERC is not a SMTP 
technical protocol requirement for SMTP communications.  It is a MAY 
and not a SHOULD, and most certainly, not a MUST.

That said, I would support the development of a formal response 
"language" to help automate the system, similar to the "SMTP Service 
Extension for Greylisting Operations" where is has been shown to have 
major benefit for timely mail delivery and DSNs for systems who have 
implemented this protocol.


Related to this, I would "mention" additional SMTP extended add-on 
protocols that have shown and have  some level of SMTP benefits.

Have a good and safe day.


On 4/8/2020 1:34 PM, John C Klensin wrote:
> Hi.
> This note is just for information and documentation -- no action
> required or requested until we have a WG.
> Thinking about my recent response to Jeremy and Timo raised
> another question about 5321bis:
> Given that the DSN extensions, the DSN model, and the Enhanced
> Status Codes are widely implemented and used, should 5321bis
> incorporate them or at least reference them normatively?   If
> the latter and maybe even if 5321bis ignores them, they are
> another candidate for inclusion in the Applicability Statement.
> The working copy of 5321bis Appendix G has been modified to add
> the above to the list.
> best,
>    john
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