Re: [ietf-smtp] Fwd: New Version Notification for draft-crocker-email-deliveredto-00.txt

[Alessandro Vesely <[e-mail]>]

On Fri 05/Feb/2021 22:53:34 +0100 Dave Crocker wrote:
> On 2/5/2021 1:44 PM, Valdis Klētnieks wrote:
>>
>> It's a plausible design that the agent doing final delivery accepts
>> responsibility for delivery to multiple local mailboxes (I've often had things
>> that ended up delivering to root@localhost and valdis@localhost with one
>> invocation of the local delivery agent, for example).


Even then, actual delivery usually happens one mailbox at a time, in a loop.


>> Should the agent generate two Delivered-To: headers, or does it *actually*
>> get generated appropriately for each copy (at a time later than when the
>> agent accepted responsibility)?

The second, IMHO.  Adding multiple Delivered-To: at once, one for each mailbox, 
would violate the MUST NOT in Section 5.


> The question for the specification is whether it makes clear what the 
> specification calls for.  I think it does, but if readers aren't clear about 
> it, it would be good to know what about it isn't clear enough.


Perhaps, the case of delivery to multiple mailboxes should be anticipated in 
Section 3.


> A different question is how to implement the specification, so as to conform to 
> the specification.
> 
> For storing a separate copy for each recipient, that seems straightforward.
> 
> For sharing a single copy of the message among multiple recipients, the answer 
> probably is not straightforward...


The case of shared IMAP folders is also straightforward.  The Delivered-To: 
contains the mailbox of that folder if it has one, or the mailbox of the 
recipient whose filter directed the message to that folder.

If the mail store implements messages to multiple recipients as files with 
multiple links, I see no way it can add a Delivered-To:.  Such a complicate 
system perhaps might resort to adding it on the fly whenever a MUA downloads 
the message.  Or it can do without.  Or maybe it may make sense to have 
something like Delivered-To: [e-mail].


Best
Ale
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