It is the entity's manager who activates, creates, deactivates, manages and deletes mailboxes.
Find more information in the FAQs:
EGT - How do you activate mailboxes in your organization? EGT - What happens when you activate mailboxes? EGT – What are the consequences of activating and deactivating mailboxes? EGT – How can you create a mailbox? EGT – How can you delete a specific mailbox?