During a coexistence migration scenario, you need to put in place a forwarding mechanism to ensure that migrated and non-migrated users can communicate with each other.

Enabling forwarding in Exchange, either through PowerShell or manually is a three-step process:

  • create a contact;
  • hide it from the address book;
  • activate the forwarding “to” the contact just created.

Using PowerShell to create a forwarder

This procedure activates forwarders for Bob. It consists of creating a contact called bobforward and enabling forwarding for bob to this contact.

  1. Create a new contact:
    New-MailContact -ExternalEmailAddress ‘SMTP: bob@domain.onmicrosoft.com’ -Name ‘bob thecontact’ -Alias ‘bobForward’ -FirstName ‘bob’ -Initials ” -LastName ‘thecontact’
    See http://technet.microsoft.com/en-us/library/bb124519(v=exchg.150).aspx for the full syntax.
  2. Hide it from the address book: set-mailcontact bobForward -hiddenfromaddresslistsenabled $true.
  3. Activate the forwarding: Set-Mailbox bob –ForwardingSmtpAddress bob@domain.onmicrosoft.com –DeliverToMailboxAndForward $false.

Manually creating a forwarder

  • In the Exchange management console, select Recipient configuration.
  • Select your user.
  • Display the user’s properties.
  • In the MailFlow Settings tabs, select Delivery Options.
  • Display the properties, and select the target contact.
  • You cannot directly enter an email address in the forward to field.
  • You must go through the intermediate step consisting of creating a contact that has the forwarding email.

You can also create the contact with the Exchange Management console or with PowerShell.
Here is an example of command:
New-MailContact -ExternalEmailAddress ‘SMTP: bob@cloudiway.onmicrosoft.com’ -Name ‘bob lecontact’ -Alias ‘bobForward’ -FirstName ‘bob’ -Initials ” -LastName ‘lecontact’

Do not check “Deliver Message to Both Forwarding Address and mailbox” because this would create duplicate messages if the mail gets delivered at the target and is then migrated by your migration solution

See http://support.microsoft.com/kb/281926/en-us for more info.