1. A method implemented by one or more processing devices, the method comprising: identifying a conflict between a first endpoint and a second endpoint that are in a sharing relationship, the sharing relationship comprising sharing a feed, wherein relationship metadata associated with the sharing relationship is shared as a file in the feed, the relationship metadata including a category identifying multiple types of data, the identifying the conflict comprising: determining a first change to a first instance of an item by the first endpoint, and determining a second change to a second instance of the item by the second endpoint before the second endpoint received an indication of the first change; and notifying at least one of the first endpoint or the second endpoint of the conflict via an email message comprising an indication of at least one of the first change or the second change.