The most important step that we need to do after a Exchange Migration from On-premise Exchange server to office 365 is to convert all the on premise Exchange mailboxes to Mail Enabled users.
What happens if we decommission on-premise servers without converting them to MEU’s
All the messaging related user information on the Cloud will be lost. Meaning which Dir-sync wont be able to find an associated target address for the users and users wont be able to connect to the cloud mailboxes which will result to an incomplete off-boarding to office 365.
Dir-sync wont be able to connect to the cloud mailbox and the user account in the DC.
Dir-sync wont be able to identify the target proxy address if we don’t have a MEU’s for the same and wont be able to locate the remote routing address.
Initially these values were stamped and provided on the on-premise mailboxes but now since we have moved all the mailboxes now we need to disable all the on-premise mailboxes, create a associated MEU’s for the same and then decommission the on-premise servers
There are scripts to help you convert mailboxes to MEUs which will make our job very easy.
•ExportO365UserInfo.ps1 Collects information from your cloud mailboxes and saves it to a CSV file. The Exchange2007MBtoMEU.ps1 script uses the information in the CSV file to bulk-create the MEUs.
•Exchange2007MBtoMEU.ps1 Conerts on-premises mailboxes to MEUs
Please follow the below link to download these scripts
If you want to change this value to single user you can use the below steps
First run the below command to get these values
$user = Get-ADUser username -IncludeAllProperties mail,department,ProxyAddresses
Then disable the on-premise mailbox
Get-Mailbox -identity $user | Disable-Mailbox -Confirm:$false
Now enable MEU for the single user
Enable-Mailuser -identity username -PrimarySmtpAddress “give the value” -externalemailaddress “give the value”
Set the associated proxy address for the single user
$user.ProxyAddresses = “set the proxy address value”
Imp Note : This article applies only for Exchange 2007 on premise and still if you bring any 2010/2013 into coexistence in onprem then don’t need to follow since it will convert the mail-enabled users to a MailUser after the remote move completes automatically.
MVP – Exchange Server