whathappenedtoyourwhitespace?

Why are you generating a DSN?  If it's for "we decided to reject it later" then 
it's your delivery pipeline post-postfix.

If it's a "user doesn't exist" I'd probably do a catchall alias per domain 
which was a pipe to a DSN generator; if you can't reject during the SMTP 
transaction.  You can still reject during the SMTP transaction of course.  I 
haven't thought hard about how to do that phase, if you're the outbound smtp 
client in postfix and the NEXT hop rejects.  We will need to figure that answer 
out I guess.  I'll see what I can write up for it.

Bron.

On Thu, Jun 25, 2026, at 05:49, Edmund Lodewijks wrote:
> Hello all!
> 
> I am trying to implement§12 of spec-03 inPhoenixDKIM(anOpenDKIMfork—
> milter pluslibrary),andthe myquestioniswhereDSNgenerationissupposed
> tolive.
> 
> Amiltercannotdoit I think:oncewe'veanswered250thesessionisgoneand
> there isnomilterintheasyncbouncepath.AndtheMTA'sownbouncegenerator
> knowsnothingaboutDKIM2—itwon'tundorecipechangesorsigntheDSNasa
> freshmessagewithmf=<>.
> 
> It wassuggested earlier on this ML (Bron?) thatyoucandothisonPostfix
> todaywithoutcorechanges,presumablyapipe/transportthatshellsouttoa
> DKIM2libraryandre-injects. This seems to be what the reference
> implementation on github is doing?
> 
> That would work,butistheexpectation indeedthateveryoperatorwirestheir
> ownpipe,perMTA?Thatfeelsfragileand inefficient, if everyone is supposed
> to go that way with DKIM2.Istheintentthatthiseventuallylandsin
> theMTAs(Postfix/Exim/Sendmail),withthepipejustastopgap?
> 
> Thank you for your time, sharing of knowledge, and energy!
> 
> Kind regards,
> 
>     Edmund Lodewijks
> 
> 
> -- 
> Edmund Lodewijks <[email protected]>
> TZ: UTC+2 / GMT+2
> 
> _______________________________________________
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> 

--
  Bron Gondwana, CEO, Fastmail Pty Ltd / Fastmail US LLC
  [email protected]

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