XLIST, special-use mailboxes

[ellie timoney]

Hi Paul,

On Fri, Jun 15, 2018, at 6:26 PM, Paul van der Vlis wrote:
> So xlist is removed in 2.5, and the new implementation is not there?
> So no support in Cyrus 2.5.10.

So, there's a few parts being mixed up here.

* The RFC 6154 IMAP LIST Extension for Special-Use Mailboxes is supported in 2.5.  My understanding is that this is the standardisation (into the LIST, CREATE, etc commands) of the functionality previously known as "XLIST".

* The XLIST command continues to work in Cyrus 2.5, but it's basically just a synonym for LIST.  Speculatively, modern clients are probably using the RFC 6154 LIST extensions these days, but we continue to accept the XLIST spelling for backward compatibility to older, pre-6154 clients.

* The `specialusealways: 1` setting exists to make Cyrus always include special-use information in its LIST responses.  The default is to only include it when it's requested.  Enabling this setting is not strictly standard compliant, but might be helpful if your users have buggy clients that want special-use information but do not ask for it.

* The `xlist-attribute: mailbox` settings in imapd.conf no longer exist in Cyrus 2.5.  This was used by the 2.4 XLIST implementation to provide special-use information.  Since RFC 6154 support was added in 2.5, special-use attributes are first class attributes on mailboxes, and are no longer faked in this way.

* The `xlist-attribute: mailbox` settings have reappeared in Cyrus 3.0 as a way of providing information to the autocreate mechanism, such that autocreated mailboxes could have their special-use attribute applied during creation.  The choice to re-use the "xlist-" name was to mainly to aid migration from 2.4 systems to 3.0, but it does cause confusion!  The 3.0 version of the "xlist-" names may be deprecated and renamed to something like "autocreate-specialuse-" in a future major release, but this has not yet happened.

Generally, to avoid confusion, I'd suggest referring to the special-use attributes and support for them as "special-use attributes", or "RFC 6154".  The "XLIST" name referred to a specific pre-standardisation implementation of a similar idea that no longer exists.

Cheers,

ellie