It does, but IMAP is clearly not a priority, and they certainly aren't interested in JMAP. They support IMAP (with caveats) because you can't really offer e-mail without IMAP, but they want you to use their GMail app.
Normally, email providers let you organize into folders. And IMAP (if I understand correctly) DOES NOT allow clients to see those folders and replicate the folder structure.
But Gmail doesn't have "folders". They have "labels". I wont go into all the details about how Gmail labels work that frustrate and annoy me, but the point is that IMAP clients cannot see labels, they can't replicate it on the client end, etc.
This caused a legitimate problem at work when the finance dept. wants to use this service that reads emails to automatically scan invoices into their system and whatnot. They wanted to be able to only have a subfolder automatically imported into the program, because too many of the emails were not relevant to get imported, creating more work to clear them out.
We were not able to achieve a solution with a simple folder for the users to move emails into to get them imported. Instead, we had to set up a second email account specifically for this importing service, and whenever finance wants something imported, they forward the email to that second account.
The problem is that in IMAP the concept of labels doesn't exist. Thus they are implemented using folders, which is a concept in IMAP. But that issue is, a message is then in multiple folders (to reflect that it has multiple labels), but in the way this happens in IMAP, they are different messages, even if the content is the same. And thus I can imagine, automated programs, not aware of this, may for example see 2 invoices (because the email has 2 labels) rather than 1.
IMAP has a concept of flags/keywords (https://datatracker.ietf.org/doc/html/rfc9051 2.3.2) and there's a whole bunch of servers and clients that support using it in a similar way as labels - Thunderbird, Zimbra, dovecot, etc.
It's not a feature originally built for labelling like Gmail, so it has a few complexities ("Servers MAY permit the client to define new keywords") and enough clients (especially mobile) that don't support it - but they could just like Thunderbird or some webmail clients.
I've used it basically exactly like Gmail labels for years on TB on desktop.
> Normally, email providers let you organize into folders. And IMAP (if I understand correctly) DOES NOT allow clients to see those folders and replicate the folder structure.
