Exchange Online will soon start blocking emails from old, vulnerable on-prem servers

Slowly but surely, Microsoft aims to make it impossible for unsupported and/or unpatched on-prem Microsoft Exchange servers to use the company’s Exchange Online hosted cloud service to deliver email. Blocking potentially malicious emails from reaching Exchange Online “To address [the problem of persistently vulnerable Exchange servers that cannot be trusted], we are enabling a transport-based enforcement system in Exchange Online that has three primary functions:

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