Re: homework, not an experiment, draft-crocker-email-deliveredto

On Wed 04/Aug/2021 16:11:38 +0200 Viktor Dukhovni wrote:
>> On 4 Aug 2021, at 8:38 am, Dave Crocker <[email protected]> wrote:
>>
>> I don't see anything in either that prohibits what you've described.
> 
> The main thing that's implicit is that MUAs can't generally expect
> to find a usable recipient address in the recorded "Delivered-To"
> mailbox.  This may be true for some operators for some period of
> time, but is not a requirement of the field semantics.


A MUA can use Delivered-To: to compare the address therein with the 
configured user addresses so that replies can have a From: field that 
matches the original recipient.  Some agents are even able to unwind 
various Received:/Delivered-To: pairs.  Obviously, internal codes or 
HMAC break such usage.  Fields reordering breaks it too.

Would it make sense to define, alternatively:


     "Delivered-To:" FWS Mailbox [CFWS] CRLF
                     ; Mailbox is from [SMTP]

where a comment may contain an opaque crypto token whereby an MTA can 
recognize itself and break mail loops only in that case?


Best
Ale
-- 

p.s. s/am email delivery/an email delivery/ in deliveredto-04