Outlook 365 not connecting to on-prem Exchange

[st84]

Hello,

in an effort to switch to a shared licensing model, we are re-deploying Office 365 via ODT.

However, after re-deploying it, Outlook just will not connect to our on-prem Exchange server but instead connects to Exchange online. 

The attached "ODT 365.zip" file contains the two files:

• configuration-Office.xml | This one was used initially, everything works fine and Outlook connects to the on-prem Exchange without issues. However, it's not shared licensing.
• configuration-Office365Shared.xml | Everything but Outlook not connecting to on-prem works fine as well.

We've already tried the registry fix mentioned here: https://techcommunity.microsoft.com/t5/office-365/outlook-365-outlook-install-does-not-see-local-exc... 

>> HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\office\16.0\outlook\autodiscover
DWORD: ExcludeExplicitO365Endpoint
Value = 1

However, that registry key does not exist in our environment. There was mentioning of a different path in the registry somewhere (can't find the link anymore), but those paths did not exist in our registry either. 

We also tried manually adding the on-prem server by manually setting up an account in Outlook. This did not work either.

So how do we manage to get Outlook 365 to connect to our on-prem Exchange server when installing it with the shared license option? We do not have a hybrid model yet and are not using Exchange online yet. 

***EDIT***

I should have mentioned this is in a VMware Horizon Instant Clone environment. 

Thanks!

[#2]

I believe I found the issue...will do some more testing to be sure and update this thread accordingly.

[#3]

The solution/workaround in our case was to disable the 'Exchange Online' app in the users licensing tab:

As soon as that checkbox is unchecked, Outlook will connect to the on-prem Exchange. 

This works for now. However, it would be convenient if this could be disabled at a group or license level, instead of having to go into each users settings and disable it. Perhaps there is an easier way?

[#4]

@st84 Sorry guys for replying to an older thread but we have right now exactly the same issue. We have with the mail account online exchange deactivated AND did the Reg edit workaround but still the pc is not connecting to our on premise exchange server. Any other ideas?

[#5]

@CRHrchLenn anyway to fix this issue with exchange outlook combo on windows desktop client, e.g. windows 11 + outlook? Exchange server always defaults to office 365 online but never goes to on premise server directly.  I can connect to my microsoft exchange server active sync no problem in windows and my iphone 14 pro mac to on premise exchange client works fine via my apple iphone mobile.  Microsoft exchange active sync connections so that's a work around i guess but it should work as advertise, how to get microsoft exchange server to connect to on premise with custom domain name should be the title, i did enable autodiscover and DNS so that works but still does not work connecting exchange outlook to on premise, it just uselessly defaults to office 365 online and that's not even my exchange server domain!!

[#6]

@st84 

What is the MX record pointer and Email flow expected?

[#7]

@Kidd_Ip autodiscover is DNS, not mx. Mx is only todo with mail flow.. that works great.

Autodiscover DNS connect to on premise exchange from local IP.. in windows mail, autodiscover at Present  only defaults to office 365 not on premise.

[#8]

@quantumleap955 

Well, take a look at this, I thought what you mentioned was DNS A record and I would prefer to make sure MX record under DNS, without understanding the end to end Email flow, it may hard to locate and solve the issue, MX record may help to isolate the issue from on-prem or on Cloud such as DNS, Email gateway, security setup

https://o365info.com/autodiscover-flow-in-an-office-365-environment-part-1-of-3-part-29-of-36/

https://learn.microsoft.com/en-us/microsoft-365/enterprise/external-domain-name-system-records?view=...