You can customise the restrictions on how people can access your site, to do this:

• Navigate to the Dashboard
• Select User and Analytics
• Choose the Users tab
• Click Registration Options

There are multiple options you can choose from that change the restrictions on Registration, these include:

• Require users to verify email address - Users will have to verify there given email to be able to access your site
• Users need admin approval - Each user will need individual approval to access the site
• Only allow users that match Emails Allowed rules - Users email must adhere to the Emails Allowed section. This allows the admin to restrict emails to a certain Domain or Email Address
• Allow custom usernames - Allows users to set there own usernames

Click the green Update button at the bottom of the page.