Give others access

On the Settings tab you'll find the Shared with card. There you can give, for example, an IT consultant access to the email service without them joining your company. How it works is explained in Users and sharing.

Someone the email service has been shared with can create accounts, create new passwords, change names and create aliases, lists and forwarding. They can't delete accounts, aliases or lists, remove members from a list, upgrade storage or cancel the service. That's reserved for the company that owns the service.