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.
Exchange On-Premises
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
Windows
Windows | Windows Outlook clients | |||||
MS 3651 | Outlook 2021 | Outlook 2019 | Outlook 2016 | Outlook 2013 | ||
Server | Exchange Online | All | All | All - Graph MSAL PopUp | EWS | EWS |
Exchange 20192 | All | All | All- Graph MSAL PopUp | EWS | EWS | |
Exchange 20162 | EWS/ REST | EWS/ REST | EWS/ REST | EWS | EWS | |
Exchange On-Premise | EWS | EWS | EWS | EWS | EWS |
macOS
macOS | macOS Outlook clients | ||
Office on Mac (classic UI) | Office on Mac (new UI) | ||
Server | Exchange Online | All | All |
Exchange 20192 | All | All | |
Exchange 20162 | EWS/REST | EWS/REST | |
Exchange On-Premise | EWS | EWS |
Other
Outlook clients | ||||||
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 | |
.eml mode |
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Split mode |
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3 If the email contains attachments