Adding an external user as a "Contact" allows you to perform a multitude of tasks that typically require the user to be created in your organization, such as forwarding email to it, or add the user to a distribution list.
To add an external user as a contact in your organization:
- Go to Admin Center.
- From the left-side menu select "Users" and then "Contacts".
- From the Contacts screen, select "Add a contact".
- In the contact creation screen, enter all the user's details.