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Exchange Online Protection transport pipeline

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Exchange Online Protection transport pipeline

How email flows through EOP — connection filtering, content filtering, transport rules, and the deliverability checks.

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01

The inbound pipeline

When a message arrives at your .mail.protection.outlook.com MX endpoint:

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02

The outbound pipeline

Outbound mail goes through a similar pipeline:

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03

Investigating delivery problems

The single most useful tool: Message Trace. For any specific message:

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04

Configuration surfaces

The transport pipeline is configured across:

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05

Common surprises

For mail-flow problems, walk the pipeline step by step. The fault is almost always in a specific stage; identifying which stage takes most of the diagnostic work.

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