If your email field is configured editable for users, then you may find this plugin very useful, as it forces users to reconfirm email each time they change their CB user profile email address.
Users can cancel the change of the email address and keep the old one or finalize confirmation from new email address. If the user fails to reconfirm the new email, then the old one remains.

This plugin is available for Professional and Developer users or can be purchased separately.

• First download CB Reconfirm Email plugin.
• Log in to the backend of your site, go to Community Builder Plugin Management and press Install CB Plugin.
• After successful installation do no forget to publish it.

From tab parameters you can set it up as you wish.