Microsoft provides a remote testing facility for their Autodiscover service. It can be very helpful.
https://www.testexchangeconnectivity.com/
Here’s some recommendations for how to use the Remote Connectivity Analyzer:
- If you CAN NOT make the autodiscover work here then we won’t be able to make it work either.
- If you CAN make it work here then we should be able to make it work.
- If this autodiscover test works for you, you may still have problems on your local LAN. This can happen if you have an incorrectly configured on-premises (Exchange) autodiscover configuration and service. Even if you have clients running on-premises that are successfully connecting to Office 365 it can still be a problem for cloud-configured Office 365 accounts because the environment is a hybrid one.