Ok, I worked on this a few years ago. I don't remember the details but I think I ran into some problems. I don't think I ever filed an enhancement bug for this. I think this allows any imap folder that is set to "check this folder for new message" to also mean use IDLE for this folder and don't release it for other purposes. So here's the WIP diff. I may attempt to revive this if nothing else supersede.
Bug 1726379 Comment 1 Edit History
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Ok, I worked on this a few years ago. I don't remember the details but I think I ran into some problems. I don't think I ever filed an enhancement bug for this. I think this allows any imap folder that is set to "check this folder for new message" to also mean use IDLE for this folder and don't release it for other purposes. So here's the WIP diff. I may attempt to revive this if nothing else supersede. P/S: Of course the attached diff it *totally rotten* and won't merge and is attached only as a possible re-starting point.