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Many connections are being made by external sources which is generating a lot of network traffic. How do I allow internal relaying for my domains but block external relaying?
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Many connections are being made by external sources which is generating a lot of network traffic. How do I allow internal relaying for my domains but block external relaying?

SMTP relay server

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.