Migration from EWS to Graph API
Back in August 2018, Microsoft announced that there will not be any active investment in EWS APIs for Exchange Online, therefore it is strongly recommended to migrate your EWS apps that access Exchange Online to Microsoft Graph.
Firstly, enable Graph mode for your Cronofy application.
Once the Graph API feature is enabled, your IT Admin has to go through the authorization flow, the same way they did for EWS. This will create a new Graph Service Account for your tenant.
Then, using the new Graph Service Account you need to re-request access to all users’ email addresses. Please note that no duplicate accounts will be created during this migration. If you are trying to re-authorize an existing account, we will detect this old Exchange account and link it under Graph Service Account.
Finally, with everyone connected via the Graph Service Account, you should revoke access to the old Exchange Service Account. This will clean up the original account and authorizations, ensuring all connections are now handled via the Graph Service Account and API instead.
If all looks good on your end, your IT Admin can then delete the Exchange Service Account from your Exchnage server.