There are 2 types of mailboxes:
The global mailbox, which is automatically created once mailboxes are activated in an entity, and which has a number of characteristics that differentiate it from other mailboxes.
The other specific mailboxes, which are subsequently created following a specific organizational logic. Therefore, before setting up your organization's mailboxes, it's a good idea to spend some time thinking about the logic and organization that best suits your organization's needs.
Find more related information at:
EGT - What are mailboxes?
EGT - What are the characteristics of the global mailbox?
EGT - How do you organize your organization in mailboxes?