Mailbox '<UserName>' in the source forest is currently enabled for Unified Messaging but it can't be enabled for Unified Messaging in the target forest for the following reason: An extension number can't be generated for the user. To configure an extension number, use the -Extensions parameter with one or more valid extension numbers. Please fix the problem or disable the mailbox for Unified Messaging before you try the operation again.
The New-MoveRequest cmdlet that's used in the mailbox move procedure performs some validation actions. One of these actions is to check whether the source mailbox is enabled for Unified Messaging. To confirm that this is the issue that you're experiencing, check whether the source on-premises mailbox has a proxy address that contains an "EUM" (uppercase letters) prefix. To do this, follow these steps:
- Open the Exchange Management Shell, and then run the following commands:
Get-mailbox email@example.com |select -expand EMailAddresses
Get-UMMailbox firstname.lastname@example.org |fl
- Examine the output. If the mailbox is Session Initiation Protocol (SIP)–enabled, the mailbox should have a primary "EUM" (uppercase letters) proxy address and a secondary "eum" (lowercase letters) proxy address. If the primary EUM address is missing, you've confirmed that this is the issue that you're experiencing.
Article ID: 3142072 - Last Review: Dec 21, 2016 - Revision: 1