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Define &quot;express&quot; migration, did you opt-in to install the AAD Connect tool or just did the one-time sync? And if you installed it, did you make any changes to the default config and/or sync rules?<br />
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What is the value of the on-premises userPrincipalName attribute? If it's populated with the same domain.com suffix, it should be correctly synced to O365.
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ajdratch

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I had the option for &quot;Cutover&quot; or &quot;Express Migration.&quot; I choose Express Migration. <br />
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I did install AAD connection tool and it is running now. The only change i made to the default was specifying the OU to sync. <br />
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I can sync and migrate accounts and they will pick up all the user's email addresses but it will not change the username to match the Primary Address. The &nbsp;username is still user@domaincom.onmicrosoft<wbr />.com<br />
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The Windows domain is domain.net. They do not own that so it is not getting migrated to Office 365. The user's principal name firstname@domain.net. Their primary email address is firstname Lastname@domain.com
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I changed the UPN to match the email address in Attribute editor, ran the sync and it updated the login name. <br />
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This did work for users who were already sync'd.<br />
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I was on the phone with Office 365 support for over an hour and it was obvious they did not have any ideas. <br />
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Thanks so much
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I am setting up a client on Office 365. I'm doing the express migration. &nbsp;All the accounts have sync’d. <br />
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I started migrating a couple of accounts and the migration works. Their mailbox is created and they have all their aliases assigned to their account. <br />
The problem is the login user name is username@domaincom.onmicro<wbr />soft.com and I can’t change it. <br />
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Their primary SMTP address is user@domain.com. It shows this is the primary address on-prem and when I look at their mailboxes in Exchange Admin Center online. <br />
I need to figure out how to get this to change so their primary email address is also their login address before I can migrate any more users.
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I am setting up a client on Office 365. I'm doing the express migration.  All the accounts have sync’d. 

I started migrating a couple of accounts and the migration works. Their mailbox is created and they have all their aliases assigned to their account. 
The problem is the login user name is username@domaincom.onmicrosoft.com and I can’t change it. 

Their primary SMTP address is user@domain.com. It shows this is the primary address on-prem and when I look at their mailboxes in Exchange Admin Center online. 
I need to figure out how to get this to change so their primary email address is also their login address before I can migrate any more users.

Office 365 change login from onmicrosoft.com to domain.com

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.