Accounts are unique when connect as accounts to Nylas, the same applies for accounts connected to the dashboard. You need to create new accounts and delete your old ones.
- Log in with your old domain / alias
- Invite the account on the new domain
- New Account on new domain > Accept the invite
- Make that user an Admin
- Then invite new accounts on the new domain
Email addresses are unique, when you log in with your new domain it will create a new account.