I have an interesting idea. Similar to the "?" function, you could include a function to be an unlocking mail guide. The icon could be a ✉, be above or below the scene map button and have the same character icons on the left of the screen as the "?" layout. If you want to unlock a specific mail like Alex's "Clothes that 'Fit'" clicking the mail lock icon will say "Tracking mail", the map will have a ✉ on the "Forest with Alex" square by the red and purple corruption points small circles. In the "Forest with Alex" section it will have an ✉ on "Talk Normally" then "Why aren't your pants done up?" If it is an already unlocked mail it will be 
The picture shows that at noon on Saturday I selected "Forest with Alex" and unlocked one of the two available mails