Shared, offline folders in Mailbird

I've just started using Thunderbird and I find it a bit slow at times, however it does two things I really need:  1, work with multiple account inboxes; and 2, allow me to save email to a set of offline folders (which I can drag and drop email to from any inbox).

I've tried Mailbird, which I really like the usability and speed of, and it let's me use several accounts, but I can't see any way of having a set of off-line folders that I can save email (from all accounts) to.

Is there a way to set this up that I just haven't found?

What I don't want to do is just save individual email and throw them into a folder structure (of dozens and dozens of folders) through a mechanism that's more like email export.  Alternatively, I could live with being able to drag-n-drop email between folders of different accounts by having one account with a set of folders and moving email into that.  I already have one master account to go with the half dozen individual accounts that people I support (family) have.