Update 3/27/2025: We updated the "Access to public folders" section below.
This post is a part of our EWS (Exchange Web Services) to Microsoft Graph Migration Guide Series.
In 2018, we announced ...
Updated Mar 27, 2025
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We are software developers, and we are currently evaluating the possibility to migrate our VSTO-based Outlook add-in to the new, JavaScript-based "web add-in" format, since VSTO-based add-in will no longer be supported in "the new Outlook".
To summarize:
- Exchange Online only supports MS Graph, not EWS,
- on-premise Exchange only support EWS, not MS Graph, and
- some things that were possible in VSTO-based Outlook add-ins (e.g., completely downloading the currently selected message in eml format) require back-end calls (to Graph or EWS) in JavaScript-based web add-ins.
Correct me if I'm wrong, but won't that mean that Outlook add-in developers will, in the future, always have to develop *two* versions of their add-in backends? One exclusively for Exchange Online (with MS Graph), and one exclusively for on-premise Exchange (with EWS)?
If that is the case, the conclusion that "Outlook is not affected" might be a bit premature...