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Exchange ActiveSync (EAS) is not supported anymore in Outlook 2016

On a regular basis Microsoft is releasing upgrades for Office Desktop applications, most of them comes with a lot of benefits that makes things easier but some of them are just not that good.

Let me give you some details about Exchange ActiveSync and what it does.

Exchange ActiveSync is a client protocol that lets you synchronize a mobile device with your Exchange mailbox. Exchange ActiveSync is enabled by default when you install Exchange 2016. Exchange ActiveSync is an Exchange synchronization protocol that's optimized to work together with high-latency and low-bandwidth networks. The protocol, based on HTTP and XML, lets mobile phones access an organization's information on a server that's running Microsoft Exchange. Having said that Exchange ActiveSync lets mobile phone users access their email, calendar, contacts, and tasks, and lets them continue to access this information when they're working offline.

For now all seems to be clear and right. What is the issue then? The problem occurs because Outlook does not support connections to a server that is running Exchange Server by using the EAS protocol and when you configure Microsoft Outlook to connect to Microsoft Exchange by using the Exchange ActiveSync (EAS) protocol, you receive the following error message:

Log onto Exchange ActiveSync mail server (EAS): The server cannot be found.

It seems that Microsoft is forcing us to use their email services trough Exchange Online if we are getting the software trough an Office ProPlus subscription or any other Office 365 plan that includes it.

Let me give you an example of how this almost ruined a project of one of our company's customer due to this new "UPGRADE" Microsoft released with Office 2016.

A Customer is migrating from a Hosted Exchange email provider to Office 365 (Exchange Online) but the migration also includes to upgrade their office desktop applications. so we created the project plan and defined that before the migration we will upgrade all their office apps to be compatible with Exchange Online since they had outlook clients that are not compatible with exchange online (another Microsoft Improvement) however, we started the deployment of Office 2016 and then we faced the observed issue while we tried to connect Office 2016 to their previous Hosted Exchange Server (Since them migration haven't been even started). You can think, Why you just didn't change your AutoDiscover DNS Records? or Why you just didn't force to connect to your Hosted Exchange? well, let me tell you, I did It!, I tried any possible way to force Outlook 2016 to connect to the Hosted Exchange without success and that is how I learned that Autodiscover, EAS and any other set up don't work anymore. And based on that this was not an easy thing to fix for me I created this article to help anyone else that is having this issue or is working on a migration.

But, don't worry! nothing has been lost, below you have the solution to fix this behavior:

The list below (ignore the DWORD values) is the method Outlook 2016 tries to contact the Autodiscover service of an Exchange Server with Client Access Server (CAS) role. The Outlook client will go through one or more of the methods below to get the mailbox information. Due to the situation where the Outlook 2016 clients need to connect to the Hosted Exchange Server right away, and the domain has been validated already in Office 365 tenant, the recommended action is to add the registry entries below to force the machines within the domain to lookup for the Hosted Exchange Server Autodiscover service, and prevent the clients from connecting to Office 365 Exchange Online. This is just a stop-gap in preparation of migrating the email from hosting services to Office 365.

Then just open outlook and lets provide your credentials to be able to connect to your Hosted Exchange server.

Once you have completed the migration I assumed you will now require to be able to connect to Exchange Online to set their new profile, for that, lets just delete the keys we added and lets open outlook and the new Outlook to Office 365 set up account wizard will pop up to get you easily connect to Office 365.

Further information is available from the link below:

https://support.microsoft.com/en-us/help/2212902/unexpected-autodiscover-behavior-when-you-have-registry-settings-under

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