Re: [ietf-smtp] SMTP status codes 251 and 551

[George Schlossnagle <[e-mail]>]

On Mon, Feb 10, 2020 at 3:11 PM John Levine <[e-mail]> wrote:

> In article <644DAD60BFC9A9FC2C84194A@PSB> you write:
> >...  I can actually see some advantages for organizations that divide up
> >their internal mail systems by laboratory or country (and
> >pressure to do the latter from privacy law differences) when
> >people make intra-company moves.   But, no, one cannot get rid
> >of them on the basis of "never implemented or deployed".
>
> That's not what I was planning, although it might be interesting to
> try returning some 251 codes and see how well it works.
>
> For an article I'm writing, I'm figuring out what to say about the
> slow demise of mail forwarding.
>

We see a good bit of email here and the number of 551s that seem to
indicate forwarding is being suggested is incredibly tiny.  I could run
some stats if you like, but call it < 0.0002% over the past year's bounces.

Email being what it is, there's lots of use of 551 for other purposes
(anti-abuse feedback, etc).

George