If you have the legacy free edition of G Suite, upgrade to Google Workspace to get this feature.
As a Gmail administrator, you can turn on alerts for messages that include external recipients. Gmail shows these alerts when your users get a message from an external email address, and when they reply to a message that includes an external address.
The alerts help people avoid unintentional replies to recipients outside your organization. They also remind people to treat external messages with caution.
When this setting is on, Gmail shows:
- External message warnings when an email thread includes email addresses outside your organization.
- External reply warnings when you reply to an external email address that isn't in your organization's Directory, your personal Contacts, or other Contacts.
Gmail doesn't show these warnings for secondary domain or domain alias addresses.
Note: When you compose a new message to an external recipient, Gmail always adds an image or colored border to the email address. This warning can't be turned off with the Warn about external recipients setting.
Turn external recipients warnings on or off
From the Admin console Home page, go to AppsGoogle WorkspaceGmailEnd User Access.
Tip: To see End User Access, scroll to the bottom of the Gmail page.
- Select your top-level organization.
- Scroll to the Warn about external recipients setting.
- Click the checkbox to turn warnings on or off.
- Click Save.
It can take up to 24 hours for your users to get these alerts after you turn them on. You can monitor settings changes in the Admin console audit log.