Hi - long time lurker, very rare poster
I understand Dovecot's support for mbox quotas is - well, not quite there yet. But I actually am not asking about that. I use vpopmail and qmail and Maildirs and was wondering about the QUOTA imap extension, which allows IMAP clients to query their quota settings.
The reason I need to know about this is that I have a mailserver with a chunk of clients and their mail stores are getting large. And starting to exhaust my storage. I could just throw more storage at it - but they're not paying me for that level of storage, so I need to quota them. And my main source of business is one particular consulting company, so I pretty much have to do what they say, within reason, and they said, "Okay, you can quota everyone, so long as they can at least find out what their quota is in Webmail..." Which is pretty reasonable - quota'ing people and then not letting them know how close to their quota they are seems cruel, especially with the meager IQ's of my particular set of clients.
Some research on my part has determined that there's an RFC for a QUOTA extension to IMAP, and there are plugins for my webmail program (Squirrelmail) which can display the user's quota usage there. Also, some mail clients are smart enough to also query the QUOTA extensions and let the user know how close they are to their max quota usage.
I'm also planning a pretty decent-sized technology transition in the near future (switching to a shared-storage system with two servers, etc, etc), and I could be convinced to perhaps try and change my quotaing system at the same time - for instance, switching to filesystem quotas instead of vpopmail quotas, if that will help.
The scary possibility that I guess I have to prepare myself for is that dovecot Just Doesn't Do It, and I need to figure out some other way of informing the clients of their quota usage - possibly a script that goes and recurses through maildirs and sends little emails if users are at a certain percentage of their actual usage, or something...I'm certainly not looking forward to writing that, but it's not a fate worse than death...