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[ietf-smtp] Submission DATA reply to indicate auto-save

2013-04-10 16:22:21
GMail's submission server saves all the submitted mails to the sender's Sent 
mailbox. After this most IMAP clients with their default configuration will 
again save the same mail to the Sent mailbox. I'm not sure if GMail removes one 
of them as a duplicate or not. I've been considering doing a similar feature to 
Dovecot (it will most likely have a proxying submission server in near future), 
but it would be nice to tell the SMTP clients that this auto-saving is 
happening, so they could skip the IMAP APPEND part with default configuration.

Of course there are the LEMONADE extensions that are supposed to solve this 
same issue, and Dovecot will support those as well, but I think it's going to 
take a while for clients to actually implement those. There's likely much 
better chance of them implementing a small check for "oh, the mail was already 
saved, I'll just skip the IMAP APPEND." Even if any clients themselves didn't 
implement this, it would make it possible to implement a simple SMTP+IMAP proxy 
locally that catches the flag and supresses the APPEND before it reaches the 

So, any thoughts on creating an RFC for this functionality? I'm not familiar 
enough with SMTP yet to know what would be the best design for that 
notification. Maybe a new extended status code? Maybe change some of the DATA 
reply's text part to have a special meaning? A simple flag is enough I think, 
because it's reasonable to require that both the server and client supports 
IMAP SPECIAL-USE to find the \Sent flagged mailbox. Returning IMAP 
UIDVALIDITY+UID could help IMAP clients a bit more, but that's maybe a bit too 
ugly (and not always possible).

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