The Outlook add-in uses Exchange Web Services (EWS) or the Outlook REST API to retrieve data from the user's Outlook mailbox.
Below you can find the availability of the EWS and REST API for every supported Exchange Server / Outlook client combination and their impact on forwarding.
The REST API is the newer interface and offers more possibilities in comparison to EWS. The limitations of using EWS are listed later in the article.
For all Exchange On-Premises servers (no hybrid deployment) we can only support EWS.
Exchange Online/Hybrid Server Deployments
For Exchange Online and hybrid deployments of Exchange Servers, the following client/server combinations for EWS and REST API are available:
REST: REST API only
EWS: EWS only
Graph: Graph API only
All: EWS + Rest API + Graph API
|MS 3651||Outlook 2021|
|Server||All||All||All - Graph MSAL PopUp||EWS||EWS|
|All||All||All- Graph MSAL PopUp||EWS||EWS|
|EWS/ REST||EWS/ REST||EWS/ REST||EWS||EWS|
|Office on Mac (classic UI)||Office on Mac (new UI)|
|Android App||iOS App||Web Browser (Exchange Online)||Web Browser (On-Premise)||Mobile Browser|
|Server||Exchange Online||Graph/ REST||Graph/ REST||All||EWS/REST||not supported|
|Exchange 20192||Graph/ REST||Graph/ REST||All||EWS/REST||not supported|
|Exchange 20162||REST||REST||EWS/REST||EWS/REST||not supported|
|Exchange On-Premise||not supported||not supported||n/a||EWS/REST||not supported|
1 Microsoft Office 365 subscription
2 connected to Exchange Online (hybrid deployment)
Graph MSAL PopUp: Every time a user opens the Phishing Report Button, the user will see a flash of a MSAL pop-up for logging in the user via Graph
Differences in forwarding via EWS and REST/Graph API
Forwarding can be done in “.eml” or “split” mode. Depending on the available API and the configured forwarding mode, the following files are forwarded to the customer’s email addresses:
|via Rest / Graph||via EWS|
3 If the email contains attachments