Perform these steps to prevent users from inviting guests:
- Navigate your browser to https://portal.azure.com.
- Sign in with an account in Azure Active Directory that has the Global administrator role assigned.
- Perform multi-factor authentication when prompted.
- In the left-hand navigation pane, click Azure Active Directory.
- In the Azure Active Directory pane, click User settings.
- Follow the link to Manage external collaboration settings:
- In the External collaboration settings pane, select No to Members can invite and Guests can invite.
- Click Save at the top of the pane.