Outlook rest api for on premises only setup

Question

I am trying to compare the usage of EWS vs Outlook REST Apis for an application that needs to connect to an on-prem exchange server. From what I understand, Exchange 2016 onwards supports REST Apis which are leveraged by Graph APIs as well internally when it determines that the mailbox is on-prem.

My question is, is there any way my application directly use the REST APIs to talk to the on-prem exchange, similar to EWS, if I dont need to support cloud \ hybrid setups?

For example, can I use https://my-on-prem-exchnagehost/api/v2.0/me/messages to connect to and talk to my-on-prem-exchnagehost?

All resources about the Outlook REST APIs talk about a hybrid deployment but non about on-prem only setups. My intention is to use one implementation for both on-prem and cloud where just the API endpoints change in the application, example https://my-on-prem-exchnagehost/api/v2.0/me/messages for on-prem and https://graph.microsoft.com/api/v2.0/me/messages for cloud.

Answer 1

Yes, the REST APIs should be accessible on an on-prem server. Documentation here. Note that the Exchange REST API and the Graph APIs are different and it's not a drop-in replacement with the Graph's interface.

Answer 2

You should note that currently it is NOT supported to use the REST APIs in a pure on-premises environment. It may work (you can fire requests at the /Api endpoint and may get results), but if you hit any issues you are on your own. Until Microsoft announces support for on-premises (which at the time of posting has not happened; I am not aware of any plans to change this), then you should not use it.