UPN mismatch and Exchange online

Question

Hi All,

I am planning migrate my Exchange 2016 on-prem to EXO.

i have a major concern in UPN setup in our environment.

currently UPN is set up as employeeid@publicdomain.com
SMTP= firstnamelastname@publicdomain.com

i would like to know what could be the impact if didn't change the UPN similar to SMTP and migrate the mailboxes to the cloud?

is there any impact to autodiscover?
is there any impact to Teams meeting rooms?
any impact to hybrid setup/mail flow?

Answer 1

You should set the UPN to match the primary SMTP address now. its recommended and will make your life and the your employees lives better down the road :)

Reason? This way they know their logon name since it matches the primary. Also, this ensures no duplicate conflicts down the road with other accounts.

https://learn.microsoft.com/en-us/windows-server/identity/ad-fs/operations/configuring-alternate-login-id#applications-and-user-experience-after-the-additional-configuration

Answer 2

@Andy David - MVP

Thank you.

Yes i went through the article prior to reach to community. Microsoft doesn't articulate the downstream impact if UPN doesn't change to SMTP. For an organization to put an effort and spend money on to change UPN need valid justification which is missing from Microsoft articles.

"Reason? This way they know their logon name since it matches the primary.- This is mainly for user inconvenience" this doesn't help for an organization to change all LOB applications authentication mechanism.

"Also, this ensures no duplicate conflicts down the road with other accounts.- We have Empid as the UPN prefix and the public routable domain name suffix. Hence Empid won't be duplicated at any cost." How i will justify with these assumptions for an organization to spend money to change the authentication mechanism. "

In addition to that, UPN suffix on On-prem AD is publicly routable DNS name which has been verified on M35. Both SMTP and UPN suffix domain names are same. We can't consider email as an alternative login as PC are moving towards to Hybrid domain joined.

Do you have MS or any other articles which clearly articulate UPN mismatch to SMTP downstream impact to M365 services such as EXO, SPO, Teams and Etc?

Answer 3

I dont know if there is a comprehensive article that lists the possible impacts. I have always seen it as a recommendation as it keeps things simpler for both the users an admins since they know it matches. In the past Autodiscover wouldnt work right in Outlook if they didnt match -which has now been fixed I believe ( There may be clients now that wont work if that is the case )

So really, if your org chooses not to match them, I think you are prob ok for the most part, but you may encounter some clients or some issue down the road where it may causes an issue.

Answer 4

@sanka perera

Here are two articles which may be useful to you:

• Office 365 – Why Your UPN Should Match Your Primary SMTP Address
• Why you need to fix mis-matched UPNs and SMTP addresses before you migrate to Office 365
  Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

If all users in your organization could distinguish the role of two addresses, you could keep using it although this is not recommended.

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

---

Answer 5

You probably arent going to find a Microsoft article like that. Its a recommendation, not an absolute requirement. If they dont match, things will still work, but if you run into any issues because of it, Microsoft will simply tell its recommended to make them match :)