Here’s one feature I miss from Thunderbird:
I have multiple Google accounts. These all create lots of IMAP folders, but I mostly use the Inbox folder in each account.
Currently (eM Client 3.0) I can see a combined view of all the Inbox folders in Global Folders. This is OK, but I would prefer if this could be expanded to show all the separate Inbox folders from each account, gathered together in one place.
My reasoning: some accounts are more important than others. My spam-catcher account always has lots of unread items. I need to see the unread count for each account in order to decide whether to stop work and check my email.