If you are not cutting over an entire domain/organization at once by changing the MX records, you can perform a phased migration and set up coexistence by setting up forwards on the mailboxes you wish to migrate.
This can be done either through the use of PowerShell scripts, or through your Exchange Management Console.
Note: We do not recommend setting up Exchange email contacts and a DNS Internal Relay for this, since this will not allow for any Delta Migration passes to be made afterwards because the mailbox no longer exists.
1) By PowerShell:
Here is how to do this via PowerShell:
Forward email to internal recipient and DON'T save local copy.
PowerShell command syntax:
Set-Mailbox -Identity <Identity> -ForwardingAddress <Office 365 User Email Address> -DeliverToMailboxAndForward $False
- Example: Set-Mailbox -Identity John -ForwardingAddress Suzan@o365info.com -DeliverToMailboxAndForward $False
- Because you set DeliverToMailboxAndForward to false, a copy of the email will NOT be kept in the on-premises mailbox. When setting up forwards, make sure that you do NOT save a local copy before the forward. If you do save a local copy, then when you peform Delta passes, MigrationWiz will migrate the items that it previously hasn’t migrated (and watermarked). This will cause duplicates at your Destination.
- The email address specifed on the 'ForwardingAddress' parameter should exist as a Mail Contact.
2) Through Exchange Management Console:
The first step is to create the forwarding objects in your local Active Directory. These forwarding objects will be hidden from the address book, and will be used purely to forward mail for mailboxes that are migrated. Note that these objects are created but not used until you set the forwarding, so these steps can be done ahead of time.
- Download our script to create forwarding objects to a computer that is joined to the domain.
- Modify the script in a text editor (like Notepad) and change the forwarding domain in the top of the script to the temporary domain in the new environment, for example, company.onmicrosoft.com.
- Run the script. You will know the script is complete when you see a confirmation.
The next step is to set up forwarding for mailboxes prior to migration. Before submitting a mailbox for migration, set the forward by performing the following:
- Launch the Exchange Management Console from the Start Menu.
- Expand the Recipient Configuration note from the navigation tree.
- Click on the Mailbox node from the navigation tree.
- Right-click on the mailbox to set the forward for and click Properties.
- Click the Mailbox Flow Settings tab.
- Select Delivery Options and click Properties.
Note: Do not select the option "Deliver message to both forwarding address and mailbox". This is important to ensure that Delta passes do not cause duplicates. If you do save a local copy, then when you perform Delta passes, MigrationWiz will migrate the items that it previously hasn't migrated (and watermarked). This will cause duplicates on your Destination.
- Click the checkbox Forward to, then click Browse.
- Select the name of the user that contains the prefix (External Forward) in the display name. This is the forwarding object created previously.
- Click OK.
- Click OK.