GMail-like user labels in IMAP/dovecot, situation in 2017?

[Timo Sirainen]

On 10 Jan 2017, at 21.00, Gioele Barabucci <gioele at svario.it> wrote:
> 
> Hello,
> 
> I am in the process of updating my IMAP dovecot installation and I was
> wondering what is the current state of the art for GMail-like
> user-defined labels.
> 
> Are GMail-like user-defined labels now somehow achievable with dovecot?

I think the main difference between folders and labels is that with folders you have separate flags for a mail in each folder, while with labels there's just one global flags/labels status for the mail. Every other operation can be mapped 1:1 pretty nicely. So the big question is how should this be implemented in a way that allows both regular IMAP access and also label-like access. There are two choices:

a) Implement a new storage format where all the mails are in a single physical folder. Treat flags as labels. When accessing with IMAP, create virtual folders based on the flags. This is how GMail works.

b) Implement a way to export the current folder-based storage using labels. This could be done with a virtual "all mails" folder, which combines both message flags and folder names into labels for the mails. It also likely means that changing a label changes the flag in each physical folder where the mail exists in. This is what we were planning to do for the Dovecot GMail API support.

There are some initial patches for b) that would make it efficient to implement, but they don't work right with replication or with obox format, so they didn't get merged. I think I had some thoughts on how to make them work with a different design, which I probably still have somewhere written down.

In any case, priority for GMail API support has dropped pretty low. Most people didn't really care about actually having GMail compatible API, but more about having some kind of a HTTP API. So the plan right now is to add support for JMAP, which also requires support for thread IDs like GMail does, but doesn't require support for labels.

> If now, what is missing? Standardized metadata formats? Support in clients?
> 
> I searched the web a bit but I could not find any activity in the
> relevant IETF working groups. That seems strange to me, because the
> user-defined labels looks like a feature many users would like to have.
> I suppose I haven't found the relevant discussion group. Is this kind of
> enhancement to IMAP being discussed somewhere?

I have a feeling you're thinking about something completely different from what I'm thinking though. You know that we have user-defined flags already, right? What exactly do you want to be different?