We recently discovered a mailbox with RecipientTypeDetails of SchedulingMailbox
I couldn't see much information about this mailbox type. There were some references saying that this is created by Microsoft Booking. We aren't using MS Booking so this is unlikely the cause.
Has anyone noticed this type of mailbox before and know of what applications create this?
Yes, it's used by Bookings. You can find who/what created it by looking at the Audit log (New-Mailbox -Scheduling is the cmdlet to look for).
Thanks @Vasil Michev
I found who created it but they don't have a bookings license so I'm just a bit confused on how that is possible
There are many features that will work across Office 365 even when you don't have the corresponding license. Also, any user with enough permissions assigned can just create the scheduling mailbox directly.