Outlook categories are used by Riva to identify which contacts are currently being synchronized. Adding the configured category to a record indicates to Riva that the end user wants that specific record to be synchronized.
With Outlook for Mac, by default, when a category is assigned to a contact, all messages (including appointments) that are received from an individual whose email address matches that contact in the address book, the message is automatically assigned to the same category.
This feature is a productivity enhancement available to Outlook for Mac users and is enabled by default.
To disable the feature:
Article ID: 1344
Last updated: 07 Apr, 2016