Outlook 2016 Exchange ActiveSync link to Exchange 2010

We are having issues with connecting one of our exchange 2010 mailboxes to a users outlook who is using Outlook 2016 from Office 365.

This is a remote user and when entering the details we get the error 'Log onto Exchange ActiveSync mail server (EAS): The server cannot be found.'
Martin AllenAsked:
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Mohammed HamadaSenior IT ConsultantCommented:
Could you please elaborate more how are you trying to connect 2010 mailboxes to outlook 2016? are you trying to configure the user on 2010's mailbox on Outlook 2016?
Is your Exchange published to the internet? Means can a user with Outlook even installed on he local machine can sync with Exchange, when the user is connected to the internet outside your network?

If your Exchange is fully published (Active Sync / Outlook anywhere) and has at least Service Pack 2, Outlook should find the server if you just enter your e-mail address...

Outlook will try to use the autodiscover mechanism to find the server. This assumes, that a public DNS record for autodiscover.yourdomain.tld exists. If autodiscover doesn't work, you have to enter the server name (FQDN) by hand. The server name should be also resolvable from the internet.

Another point is the certificate on the public interface of exchange. As it is Outlook online, I would expect (but I'm not 100% sure) that the cert has to be a public resolvable cert, so a certificate from a public certification authority.
Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Surely you have to brief more as i see you mention Exchange2010 and then O365 as well, so is the mailbox on premises Server or Cloud ?
Does webmail work fine for the account and basic functions enabled ?
If the user is on cloud then ensure the license is assigned to user

- Rancy
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Martin AllenAuthor Commented:
The mailbox that is being added is on an Exchange Server running Exchange 2010, the user is running a copy of Outlook 2016 from Office365 and is trying to connect his exchange mailbox using ActiveSync as the option for an exchange account is not available on his copy of outlook.
Mohammed HamadaSenior IT ConsultantCommented:
Why are you trying to use Activesync to connect outlook 2016 to Exchange? ActiveSync is only meant for Mobile phones not Outlook application.

Outlook 2016 enabled Exchange ActiveSync (EAS) only for use with Outlook.com.  it won't work with EAS wont work for outlook client after 2010.

EAS doesn't have all of the features that Outlook supports. so you should be using RPC over HTTP protocol or MAPI which is Exchange's normal connectivity choices for Outlook clients.

Here's what Microsoft has to say about outlook 2013 and Outlook isn't really much different when it's about EAS.
Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Why doesnt the user use the OutlookAnywhere a builtin for such connectivity, only thing to be sure is that OutlookAnywhere is working from external. If not sure check with www.exrca.com

- Rancy
Martin AllenAuthor Commented:
The OWA access is very slow so use in Outlook would be preferable does the client need changing to Office 2013 Pro Plus?
Mohammed HamadaSenior IT ConsultantCommented:
No 2013 will have the same issue as 2016. You need to use Outlook 2010 as far as I can remember it does work with ActiveSync but I am not 100% certain .
The version of Outlook doesn't really care as far as it is 2010 SP2 or later....
Even I would say, there is not an essential difference if it is a local client or office online.
Just maybe some new functionality is not fully supported due to Exchange 2010 as the backend.

Your first posts hint to connection problems, which should be shown up by the EX Connectivity Tool what Rancy posted. If this tool runs fine, you should be able to connect he client. Even you can try which combination works.
The server name has to be the FQDN, the user name depend a bit form your environment, so test the user Kerberos name (user@mydomain.tld) as well as the NetBIOS name (DOMAIN\user).

For remote clients indeed, Outlook Anywhere is the preferred choice as it allows you to work from everywhere, inside, outside and if correctly configured, the client needs only the email address and the password, everything else is delivered by autodiscover.

Most of the problems have two reasons:
a.) Wrong or missing external DNS names for your Exchange.
The external (public) name has to be registered.
The autodicover.mydomain.tld (external) should also be registered.
And you need a reverse proxy for exchange to reroute the external address to the internal address and back. Especially if your public MX record doesn't point to your own exchange, autodiscover makes the life a bit easier.
b.) Certificate issues.
The external certificate should include all external names. So the public name of exchange as well as the autodicover.mydomain.tld
If you have a local client, the local client should have the issuer root certificate in his local certification store, if it is not a public cert. For a office 365 client I would assume (but not 100% sure) that the cert has to be public anyway.

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