Powershell command to fix UPN

I need to change the UPN for all users so I can migrate to office 365. I accidentally ran a powershell command on the entire domain instead of the test OU. Now all users UPN is just the @ symbol. When I go to Properties / Accounts, user logon name is correct but instead of the .local or .com domain, I just have the @ Symbol.

I can not figure out how to replace @ with their internet domain.
ajdratchAsked:
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Vasil Michev (MVP)Commented:
A bit hard to help you without providing additional details, we cannot really guess what the domain name/UPN suffix you want to use is. But you can try something like this:

Get-ADUser -Filter * -SearchBase "DC=domain,DC=com" | % {Set-ADUser -Identity $_.ObjectGUID -UserPrincipalName "$($_.SamAccountName) + @domain.com" }

This will create new UPN value in the samaccountName@domain.com format. If you want to base the domain part on say the domain used for the primary SMTP address, use this:

Get-ADUser -Filter * -SearchBase "DC=domain,DC=com" -Properties proxyaddresses | % {Set-ADUser -Identity $_.ObjectGUID -UserPrincipalName ($($_.SamAccountName) + "@" + $(($_.proxyaddresses | ? {$_ -match "SMTP:*"}).Split("@")[1])) -WhatIf }

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Goes without saying, TEST it first, against a single user, against 2-3 more user, before running against the whole domain.

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ajdratchAuthor Commented:
Thanks so much. The first command fix it
FOXActive Directory/Exchange EngineerCommented:
Pretty Straightforward:

$oldSuffix = ""
$newSuffix = "yourdomain.com"
$server = "Yourdomaincontroller"
Get-ADUser -ResultSize Unlimited | ForEach-Object {
$newUpn = $_.UserPrincipalName.Replace($oldSuffix,$newSuffix)
$_ | Set-ADUser -server $server -UserPrincipalName $newUpn
}


ref link:  https://blogs.technet.microsoft.com/canitpro/2015/07/07/step-by-step-changing-the-upn-suffix-for-an-entire-domain-via-powershell/
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