Issue with Microsoft 365 Business & externally hosted Exchange mailboxes

Copper Contributor
We decided to switch to Office 356 for Business due to the use of a common OneDrive structure,
and have already paid for 2 complete licenses for Office 365.

We want to share Folders and Dokumencs internally in our Team/Company all with email adresses in one domain that is actually hosted at OVH
Problem is that we already had email addresses (Exchange & promail at OVH) Unfortunately, the mailboxes are now created twice, one with the Domain that is registred with OVH and a second time with M$(o365)
the users for the Office packages are also bound to xy(at) & y(at) Unfortunately, we noticed during the setup that Microsoft always prefers the Exchange mailboxes located at the Office 356 infastrcture
With a workaround (excluding the autoconfigure Office356 entry in the registry) we can now continue to use our Own OVH Exchange Mailboxes
from the original host (OVH) and skip Office 365 Autodiscover ( or set it up via autodiscover; so far so good...
Link to the Solution :

Unfortunately, the basic functionality of SHARING FOLDERS in OneDrive to members of our domain does not work,
as the invitations to the FOLDERS are only sent "internally" and never end up in the OVH mailboxes, so they are not directly
"clickable/Useable". also the to xy(at) & y(at) MSMail / or the “free Outlook” without our intervention.
We want to Use Outlook 356 fort all our Office work this was done by automation (It would be nice to at least be asked). All of these automatisms may be user-friendly for some users, but they destroy our workflow massively...
Is there an easy way to switch off/get rid of the automatically created Exchange mailboxes in the Office 365 package and use the One Drive with Shares and Invitations with our Mailboxes still at OVH or do we have to move the whole domain (
to M$ to make the OnDrive Infrastructure properly work ?

Thanks for your Ideas !
The emails we send to ***The email address has been removed for privacy reasons. *** (Exchange at OVH) ***The email address has been removed for privacy reasons. *** (promail at OVH) arrive directly at OVH and can also be sent from iPhone, Outlook on computers with the Office 365 Autodiscover solution (


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