"Working Set" mailbox in Mac Mail with Exchange

[swiftaw]

So, my work email is an Exchange account (actually Office365) which I connect to via Mac Mail. I just noticed two new mailbox folders "Working Set" and "Working Set1" that appear in my mailbox list for that account. These folders don't show up in the Office365 web interface, nor do they show up on my iPad or iPhone. They also cannot be deleted.

Has anyone else who has an exchange account on Mac Mail had these mailboxes appear recently?

 

[Stuart in Oz]

I have the same 'Working Set' mailbox - in fact I have two of them, one for each of two email accounts I have with my university.

It appears that it is a Microsoft bug, there are some discussions of the reasons why it appears in Apple Mail here: https://discussions.apple.com/thread/6351588

Unfortunately, I can't see Microsoft rushing themselves to fix a relatively minor (albeit annoying) Exchange bug that only shows up on Apple's native mail browser. :-(