By default, each conversation is assigned Medium priority in Yablo. You can change this to Low, Important or Urgent. Open the email conversation and click on Medium and select a different priority.
Everyone who has access to this email conversation will see the same priority for this email conversation.
You can also drag and drop conversations from one column to another to change the priority when the Kanban board is structured by 'Priority'.
You can also set a priority to an email conversation directly from within Outlook. More information.