Import a user into an account
You can merge two separate Fastmail accounts into the same billing account as individual users.
To merge an existing Fastmail user into your own account, go to Settings → Users & Aliases. At the bottom of the page, click Import User.
You will need the password of the user you want to merge in order to complete the process, and all forms of two-step authentication must be removed from that user's account. It is recommended to have the owner of the account physically present so they can enter their password and review the terms.