Very useful features, basic function for an imap client

I can only second that. This is a must-have feature for any serious webmail/imap client.

What makes this issue even more apparent, is that there already is a "Subscribe..." menu entry in the context menu of a mail folder, but this option is greyed out.

We're just evaluating sogo for our corporate needs and i was really really puzzled when I noticed that the Web Interface is not able to handle IMAP subscriptions.
We're using quite a lot of shared and "public" IMAP Folders representing organisational departments and we're composing our acl on that base. typically not every folder located in the specific subtrees are of value for every person in a department, so they are individually able to compose their views without clutter. This works well with our current groupware solution but doesn't work if we don't put the users in front of a "fat" desktop email client. Since our current solution has quite some other issues we're going to change it.
So i second the opinion that IMAP Subscription handling is a basic, widely used and needed feature if people should be able to use the Web Interface for their work. Please put this item on your roadmap in a near timeframe or give at some comment on this feature stating if there are any plans to realize this or give some information concerning this essential feature.

I'd vote for that too! Currently I fight with a messed up user account and checking the subscribed folders from soho would be a very helpful tool.