How can I prevent Outlook emails from being sent to external domains?

Sam Perrow 5 Reputation points

I am trying to prevent users within my domain from being able to send emails with attachments or other potentially sensitive information to any external email domains. For example, I don't want anyone in my company (with an email address) to be able to send emails with a PDF attachment to an email address outside the organization. TIA!

A family of Microsoft email and calendar products.
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Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. ChristyZhang-MSFT 21,181 Reputation points Microsoft Vendor

    Hi @Sam Perrow ,

    Welcome to our forum!

    Are you using Exchange online or Exchange on-premises?

    If so, it's suggested that you could try to use the EAC to create a mail flow rule:


    Hope the above help!

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