What this means in practice
Paid plans include a fixed number, with additional mailboxes billed monthly.
Check the current plan allowance and recurring add-on cost together before adding addresses for a team.
Practical guidance
Mailbox count depends on the plan: Go includes one, Starter includes three, and Enterprise includes ten; Free does not include mail. On paid plans, additional mailboxes cost $3 per month each. These limits describe mailbox capacity, not the storage quota for attachments, which uses object storage.
Before adding addresses, count the actual mailboxes your team needs and compare that number with the included allowance. Aliases and mailboxes are not interchangeable in every mail setup, so check the account's mailbox controls for the specific address type you intend to create. If you need more mailboxes, account for the monthly additional cost and make sure the plan is eligible. Review both mailbox count and shared storage when planning a mail deployment, since they are separate constraints.