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

AllAllAll - Graph MSAL PopUpEWS
EWS

Exchange 20192

AllAllAll- Graph MSAL PopUpEWS
EWS

Exchange 20162

EWS/ REST
EWS/ REST
EWS/ REST
EWS
EWS
Exchange On-Premise
EWSEWSEWSEWSEWS


macOS


macOS

macOS Outlook clients

Office on Mac (classic UI)
Office on Mac (new UI)


Server
Exchange Online
AllAll
Exchange 20192
AllAll
Exchange 20162
EWS/REST
EWS/REST
Exchange On-Premise
EWSEWS


Other



Outlook clients
Android AppiOS AppWeb Browser (Exchange Online)
Web Browser (On-Premise)Mobile Browser
ServerExchange OnlineGraph/ REST
Graph/ REST
AllEWS/REST
not supported
Exchange 20192Graph/ REST
Graph/ REST
AllEWS/REST
not supported
Exchange 20162RESTRESTEWS/RESTEWS/REST
not supported
Exchange On-Premise
not supported
not supported
n/aEWS/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
  • mail.eml
  • mail.eml
  • for emails greater than 500kB the add-in automatically switches to split mode
Split mode
  • body.html
  • header.text
  •  All attachments as the original files³
  • body.html
  • headers.txt
  • attachments.txt³
  •  contains information about the attachment`s name, size, type, isInline


3 If the email contains attachments