Mailboxes in forum shop...

[AnimalCrossingPerson]

Okay, so each purchasable mailbox has a limit of X messages. Am I correct in assuming the storage doesn't stack as each one is purchased, making it cheapest to go straight to the golden super mailbox?

 

[Oblivia]

Correct. They don't stack, so whichever mailbox is active in your inventory will determine how much storage capacity you have.