Microsoft Exchange provides a full
MAPI Message Store Providers
to expose the folders stored on the Exchange server
to Outlook.
When Outlook saves a message it will be written directly to the Exchange server. The server will check and ensure that the user has sufficient permissions to write the item and that the item wasn't changed by another user in the meantime.
However, the Exchange Connector only works with the Exchange Server. The Connector communicates with the server using a proprietary Microsoft protocol.
Integration between Exchange and Outlook is perfect
since Outlook as a client and Exchange as the server
are a 1:1 match.
Exchange is designed and implemented primarily as a backend for Outlook.
Anyone planning to use a ThirdParty plugin with Outlook should be aware
that those will never match the quality of the Outlook/Exchange
integration, no matter what.
Depending on the server you will most likely encounter certain constraints,
for example some servers do not support all recurrence rules support
by Outlook. Or the other way around.
The reason why real
Message Store Providers
deal better with this fact than Client Sync
scripts is that they report all issues (conversion errors, missing
permissions, missing support, etc) in realtime.
Since Outlook writes to a local PST file with "Client Sync" tools,
it will always accept everything written to it.
Issues are delayed until the sync kicks in (which can be minutes later).