Are you getting this error in Microsoft 365 Admin center when viewing mail tab of a user? And on-prem Exchange has already been decomissioned? Well, you kinda have to “fake” the migration and clear some user’s attributes:

In AD Users and Computers, make sure Advanced Features are activated (View > Advanced Features). Go to the users OU and double click on the user. Select AttributeEditor and clear the following attributes:

msExchMailboxGuid

msExchRecipientDisplayType

msExchRecipientTypeDetails

Run AD / Entra Sync:

Start-ADSyncSyncCycle -PolicyType Delta

Wait for 15-30min and now the user will get an Exchange Online Mailbox if he has a license.

References:

https://techpress.net/this-users-on-premises-mailbox-hasnt-been-migrated-to-exchange-online/

Having issue Azure AD joining a Windows 10 or 11 computer and getting error 8018000a? This script might help you. It deletes all keys except Context under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Enrollments

$EnrollmentsPath = “HKLM:\SOFTWARE\Microsoft\Enrollments\”
$Enrollments = Get-ChildItem -Path $EnrollmentsPath
$DiscoveryServerFullUrls = @(“https://wip.mam.manage.microsoft.com/Enroll”)
Foreach ($Enrollment in $Enrollments) {
$EnrollmentObject = Get-ItemProperty Registry::$Enrollment
if ($EnrollmentObject.”DiscoveryServiceFullURL” -in $DiscoveryServerFullUrls ) {
$EnrollmentPath = $EnrollmentsPath + $EnrollmentObject.”PSChildName”
Remove-Item -Path $EnrollmentPath -Recurse
& “C:\Windows\System32\deviceenroller.exe /c /AutoEnrollMDM”
}
}

References:

https://jocha.se/blog/tech/azure-ad-mdm-intune-error-8018000a

If you have deleted a user in Exchange Online that is synced from onprem and you need to restore it, you might not want to re-sync the local user. In that case you can restore the deleted user directly in Exchange Online and make a cloud only user.

Get the deleted mailbox by name and Exchange GUI:

Get-Mailbox -SoftDeletedMailbox | Select-Object Name,ExchangeGuid

Create a new cloud only user or shared mailbox and run this command:

Get-Mailbox -Identity <NameOrAliasOfNewTargetMailbox> | Format-List ExchangeGuid

Restore the deleted mailbox/user into the newly created cloud user:

New-MailboxRestoreRequest -SourceMailbox <SoftDeletedMailboxGUID> -TargetMailbox <NewTargetMailboxGUID> –AllowLegacyDNMismatch

References:

https://learn.microsoft.com/en-us/exchange/recipients-in-exchange-online/delete-or-restore-mailboxes

With the newer versions of Outlook 365, when creating a new invitation, a Teams Call link is automatically added to every meeting, which might not be wanted by some customers. Here is a quick way to disable it for the whole tenant:

Connect-ExchangeOnline

Set-OrganizationConfig -OnlineMeetingsByDefaultEnabled $false

To check out if the settings has changed:

Get-OrganizationConfig | select OnlineMeetingsByDefaultEnabled

By default, if you send a mail on behalf of a Shared Mailbox, the sent item will be saved in the user’s primary mailbox and not the shared mailbox. If you want to change it to expected behaviour, i.e. save the items in the Shared Mailbox, execute following command. This works in Exchange Online and Exchange OnPrem.

set-mailbox -MessageCopyForSentAsEnabled $True

set-mailbox -MessageCopyForSendOnBehalfEnabled $True

References:

https://learn.microsoft.com/en-us/exchange/troubleshoot/user-and-shared-mailboxes/sent-mail-is-not-saved