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

2013-04-10 18:21:38
Hi Timo,
At 14:22 10-04-2013, Timo Sirainen wrote:
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

I assume that you have read Gmail's answer about the handling of the /Sent mailbox.

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 network.

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).

In the above you have the SMTP (MSA) client and the IMAP client which are acting independently. If the mail client already knows that the message has been saved to the Sent mailbox it could use the Message Submission BURL Extension to submit the message to avoid the "duplicate submission".

Suppressing the APPEND may be problematic. The MSA server can reject the submission attempt with a message mentioning the IMAP mailbox automatically used to submit the message. BTW, what you are looking for might be what behavior the mail client should set at configuration time to provide mail functionality. This means detecting the features offered on the server side.

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