Confirmation of action
When a user clicks on block or allow sender when receiving an email, a second prompt opens up confirming the action of the user. Probably a third prompt if the action is to block.
This will prevent a user from accidentally and unconsciously blocking senders. Most especially for on-the-go users who use phones heavily for their emails which has a high tendency of accidentally and unconsciously pressing "block sender" since they have a smaller screen and options for the banner are close to another app setting in the Outlook app.