This scope lets an app "View messages and other content in group direct messages that your slack app has been added to"
This OAuth permission scope works with these Web API methods and Events API events.
mpim.history - Fetches history of messages and events from a multiparty direct message.mpim.replies - Retrieve a thread of messages posted to a direct message conversation from a multiparty direct message.channel_history_changed - Bulk updates were made to a channel's historymessage - A message was sent to a channelmessage.mpim - A message was posted in a multiparty direct message channel