How Exchange ActiveSync works

The goal of Exchange ActiveSync (EAS) is to synchronize a user’s mailbox data (or at least a subset of it) efficiently to a mobile device that has limited bandwidth, battery power, and CPU. This sync might take place over a cellular data network, in which case, the network might or might not suffer high latency and frequent interruptions. It’s important to keep these constraints in mind as you see how the protocol works.

Device synchronization begins when a client contacts an Exchange Client Access Server (CAS) to request synchronization. The synchronization process requires the device to reach TCP port 443 on the Exchange CAS so it can make HTTPS requests to the Microsoft-Server-ActiveSync virtual directory, so assume ...

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