As an Organization Administrator you have the ability to manage how new members join your Organization.
Open Org Admin Page
To get to your Approval settings, select the Org Admin icon at the top of the page.
View Membership Approval Settings
There are two ways to allow a new member to join your Organization:
- Partially Open 
- Fully Open 
Select Partially Open Approval
Partially Open: Approval is only required for new accounts when an account is created via group link with an email domain that is not a part of your whitelist. When you select Partially Open, type the email domain that you want whitelisted here . To add another email to your whitelist select Add New Domain .
Select Fully Open Approval
Fully Open: There is no approval needed when someone creates an account via group link in your Organization. Learn how to invite a member to via Group Link here.