How to change change UPN without impacting autodiscover

Romain Torrecilla 1 Reputation point
2020-12-22T15:53:34.397+00:00

hello,
we recently migrated a customer from a hosted email platform to Office 365 email solution.

let's call:

when we started, their domain name @mathieu.company .com was pointing to Oldplatform.
They already have a Microsoft 365 Tenancy for desktop app licensing with UPN users@mathieu.company .onmicrosoft.com

day 1: To prepare the migration from oldplatform to O365, we added a DNS entry to the O365 tenancy. This way, we were able to change their UPN from @mathieu.company .onmicrosoft.com to @mathieu.company .com.
day 2: The next morning, all users had to re-authenticate for their Office desktop app, and that was fine.
day 3: in the morning, all emails users were sending from their Outlook desktop App never reached oldplatform, they stayed in the O365 Tenancy. External emails were not flowing to the Outlook Desktop App. Our workaround at this point was to have all users to use the oldplatform webmail. User on mobile devices did not notice any change.

Some technical people looked at the problem when it happened (and not before it happens, I know), and they told me this is an autodiscover problem.

We have another customer coming for migration with the same profile, and I would like to figure out how to change UPN few days before the email migration happens to configure everything in their tenancy (shared mailboxes, custom transport rules, Distribution Lists, aliases, resources mailboxes...)

Does anybody have a way to avoid the described impact?

thank you

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Microsoft Office Online Server
Microsoft on-premises server product that runs Office Online. Previously known as Office Web Apps Server.
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Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
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Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. KyleXu-MSFT 26,261 Reputation points
    2020-12-23T01:49:58.557+00:00

    @Romain Torrecilla

    To narrow down it, I want to confirm with you that:

    • Whether the old mail server is an Exchange server?
    • Where are mailboxes hosted now, old mail server or Office 365?
    • Which email address that used for those mailboxes now?

    The Autodiscover is used to configure Outlook automatically, the issue with send email is related mail flow, they are two different parts.

    So, I would suggest you try to create a new Outlook profile and check whether mailbox could be configured successfully.

    If the response is helpful, please click "Accept Answer" and upvote it.
    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.

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  2. Romain Torrecilla 1 Reputation point
    2020-12-23T13:52:06.703+00:00

    Hi @KyleXu-MSFT

    the old mail server was a hosted exchange. Now all mailboxes are hosted in O365 and are using @mathieu.company .com.

    The migration is done and everything is fully working.

    Our goal now is to learn from our mistakes during the preparation of the migration. Our customer had to access its oldplatform through webmail for 2 days and we would like to avoid such a thing for future migration.

  3. Andy David - MVP 147.9K Reputation points MVP
    2020-12-23T14:39:25.777+00:00

    Ok that's a different issue then
    You probably were seeing this issue

    https://video2.skills-academy.com/en-us/outlook/troubleshoot/profiles-and-accounts/unexpected-autodiscover-behavior

    Specifically, Outlook in newer builds will prefer connecting to Office 365 first.
    "ExcludeExplicitO365Endpoint"
    You can set this in the client registries to prevent that if needed and remove that reg entry once the mailbox is migrated.

    https://medium.com/jj365/outlook-issue-with-direct-connect-to-office365-352dd29de65

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  4. Romain Torrecilla 1 Reputation point
    2020-12-23T14:47:58.497+00:00

    thank you @Andy David - MVP , These links are really useful, I found them during my research.
    some of our customers are one-shot customers and we don't manage their workstation, doing a change to their registry could be a challenge.

    I think the MAPI option from the second link is interesting when we can't modify the registry, just because everything is handled by our team without end-user action.

    I'm just not sure if this is the solution.

  5. KyleXu-MSFT 26,261 Reputation points
    2020-12-25T07:32:48.197+00:00

    @Romain Torrecilla

    Verify domain in Office 365 will not change the Autodiscover lookup steps. In a hybrid environment, this autodiscover still point to the Exchange on-premises IP: 2
    Office 365 Autodiscover Lookup Process
    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.

    Do you try to reconfigure Outlook profile? Whether is it could configured successfully? You can also use the “Test Email AutoConfiguration” tool to check the Autodiscover in your organization.

    If the response is helpful, please click "Accept Answer" and upvote it.
    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.

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