dovecot - Jan 2018 - Questions about SPECIAL-USE IMAP extension

I'd like to configure my dovecot service to use the IMAP SPECIAL-USE
extension, but have a few questions for those who have used them, or
are knowledgable about its use.  Using this configuration as an example,

 	namespace {
 		...
 		mailbox xxx {
 			special_use = \Sent
 		}
 	}

Q1) Am I correct that mail client that don't understand SPECIAL-USE
extentions will behave the same way with repect to outgoing mailbox
storage?

Q2) Will SPECIAL-USE enabled mail clients switch the mailbox used for
outgoing mail from whatever it was using (e.g. "Sent Mail") to the
(new) special-use mailbox "xxx"?

Q3) Will SPECIAL-USE enabled mail clients connecting for the first
time use "xxx" for outgoing mail, auto-creating it if necessary?
Or will "xxx" be used only if the user does not manually configure
a mailbox for this purpose?

Q4) If I have an additional configuration

 	mailbox yyy {
 		special_use = \Sent
 	}

how does it affect Q2, Q3?

Thanks to any who can provide clarity on this.

Joseph Tam <jtam.home at gmail.com>

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On Thu, 11 Jan 2018, Joseph Tam wrote:
> I'd like to configure my dovecot service to use the IMAP SPECIAL-USE
well, in my experience SPECIAL-USE is just a suggestions to clients. Check 
RFC 6154 for MUSTs, you'll find only few. Hence, how the client (or the 
server) behaves in a special case is implementor-defined.

I do expect that any client supporting SPECIAL-USE honors the server 
setting (first time it connects to the server or everytime, but at least 
once) and creates the mailboxes it uses itself.

Otherwise, Dovecot can autocreate the mailboxes regardless of its use: 
https://wiki2.dovecot.org/MailboxSettings

- -- 
Steffen Kaiser
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On Fri Jan 12 2018 01:29:37 GMT-0500 (Eastern Standard Time), Steffen
Kaiser <skdovecot at inf.h-brs.de> wrote:
> On Thu, 11 Jan 2018, Joseph Tam wrote:
>> I'd like to configure my dovecot service to use the IMAP
SPECIAL-USE
> well, in my experience SPECIAL-USE is just a suggestions to clients. Check 
> RFC 6154 for MUSTs, you'll find only few. Hence, how the client (or the
> server) behaves in a special case is implementor-defined.
> 
> I do expect that any client supporting SPECIAL-USE honors the server 
> setting (first time it connects to the server or everytime, but at least 
> once) and creates the mailboxes it uses itself.
> 
> Otherwise, Dovecot can autocreate the mailboxes regardless of its use: 
> https://wiki2.dovecot.org/MailboxSettings
There was a similar discussion about this on list some time ago, about
whether or not Dovecot could utilize special use 'aliases' that your
clients may want to use by default, and Dovecot would automatically map
those requests to a single mailbox.

E.g.:

Outlook clients would see/use 'Sent Items'

Thunderbird would see/use 'Sent'

But both would be mapped to a single mailbox 'Sent' (or whatever you had
defined as the actual mailbox).

Personally I would love to see this implemented.

On Thu, 11 Jan 2018, Joseph Tam wrote:
> I'd like to configure my dovecot service to use the IMAP SPECIAL-USE
> extension, but have a few questions for those who have used them, or
> are knowledgable about its use.
Thanks to all who contributed, even if the answer was "it depends".
After configuring it, so far, so good.  One of my users did experience
some confusion, which answered my question ...
> Q2) Will SPECIAL-USE enabled mail clients switch the mailbox used for
> outgoing mail from whatever it was using (e.g. "Sent Mail") to
the
> (new) special-use mailbox "xxx"?
The answer to this is an emphatic "yes" for some clients (e.g. Mac OS
X
Mail 11.2).  This client will also relabel the actual mailbox "xxx"
with
its special-use name "Sent", which can cause confusion when discussing
which mailbox you're referring to.

One thing I didn't take into account was namespace aliasing: I aliased
the former UW imapd namespace (mail/), to conform to the current default
namespace ('').  However, the special-use configuration did not apply
to the aliased namespaces.  Will I have to copy all the special-use
configuration to all my aliased namespaces, or is there some syntax
magic I can use?

By the way, this is the IMAP incantations one can use to test special-use:

 	C: x2 LIST (SPECIAL-USE) "" %
 	S: * LIST (\NoInferiors \UnMarked \Drafts) "/" Drafts
 	S: * LIST (\NoInferiors \UnMarked \Sent) "/" xxx
 	S: x2 OK List completed (0.005 + 0.000 + 0.004 secs).

 	C: x3 LIST (SPECIAL-USE) "mail/" %
 	S: x3 OK List completed (0.011 + 0.000 + 0.010 secs).

Joseph Tam <jtam.home at gmail.com>