After your mailbox is moved to Microsoft Office 365 Dedicated/ITAR (vNext), you experience one of the following issues:
You don't receive all your email.
When someone tries to send mail to you (the newly migrated user), they receive a non-delivery report (NDR).
As part of the move process to vNext, objects are frozen in the legacy dedicated environment. If a user is not frozen correctly, MMSSPP will continue to update the targetAddress and proxyAddresses attributes, and this may cause a mail delivery issue.
Migrations from legacy dedicated to vNext are organized and configured with Microsoft deployment resources. This process involves the following steps to make sure that the migration is finished as efficiently and with as little effect on the end-user as possible:
Initial writeback process (currently manual*, and completed by Microsoft)
Some directory information (for example, msExchMailboxGuid and publicDelegates) must be transferred from the Dedicated directory to Azure Active Directory. To do this, the required information is extracted from the Dedicated directory and written to your on-premises Active Directory. From there, AAD Sync/Connect is used to transfer the information up to the cloud. This writeback performed manually and coordinated with Microsoft deployment resources in advance of migrations.
License object in vNext and provide the batched users to the EXO team (Customer)
As soon as the writeback process is completed, the customer will take steps to batch and license the objects by running the script provided by the EXO service team in the configuration documentation. Because the msExchMailboxGuid element is copied from legacy dedicated to the on-premises AD to vNext, this prevents a new mailbox from being provisioned and makes sure that the move is completed successfully.
Freezing of mailboxes (manual, completed by Microsoft)
Before the moves are submitted, the mailboxes are frozen. Therefore, the targetAddress and proxyAddresses properties are no longer updated by MMSSPP. After the move, the source mailbox will be configured by the Mailbox Replication Service (MRS) to make sure mail delivery continues. These attributes should remain permanently frozen after the migration to avoid any changes.
A group of mailboxes will be included in a migration batch that's provided by the customer to the Microsoft deployment resource. This must be completed several weeks before the mailbox is migrated so that the new mailbox can be pre-seeded in vNext.
Final migration (MRS)
The mailbox move is completed on the date and time requested by the customer.
Final writeback (currently manual*, completed by Microsoft)
Within three business days, a final writeback will be completed. The properties updated are targetAddress, msExchRecipientTypeDetails, msExchRemoteRecipientType, msExchRecipientDisplayType, and proxyAddresses.
If there is a report of mail delivery problems after the migration, you should collect the following information:
Non-delivery reports (NDRs), if available
Review the configuration of the object in the legacy dedicated environment. The object should be a RemoteUserMailbox with an ExternalEmailAddress attribute and a suffix of *.onmicrosoft.com: