Because Alfred’s letter bag gets pretty heavy, he is only capable of carrying 30 thank you letters per day and any extra letters you receive will be delivered the following day.
The number of gift cards inside thank you notes is completely random, but of course the more thank you notes you get, the higher the chance of getting a gift card! You can receive a maximum of 5 gift cards per day.
Once you have tapped "collect all" in your mailbox, the gift cards will be added to your total gift card count displayed on the front of the Gift Catalog, and the thank you notes will be discarded.