Email Migration Overview

Here's an overview of the cutover Exchange migration process. For step-by-step instructions, see Migrate All Mailboxes to the Cloud with a Cutover Exchange Migration.

Important   Before you run an Exchange migration, your on-premises Exchange organisation must be an accepted domain of your cloud-based email organisation.

1. Start a new migration using Email Migration and select one of the following Exchange migration types:
   
   • Exchange 2007 and later versions - Automatically detect connection settings with Autodiscover.
     
   • Exchange 2003 and later versions - Manually specify connection settings
     
2. After the migration service verifies the connection settings to your on-premises Exchange server and you run the migration, Microsoft Exchange does the following:
   
   • It uses the address book from your on-premises Exchange server to identify the mailboxes, distribution groups and contacts you want to provision in your cloud-based email organisation.
     
   • It provisions the new cloud-based mailboxes. Microsoft Exchange processes up to N migrations at one time, where N is the maximum number of mailboxes to migrate simultaneously that the administrator specified for the migration.
     
   • It creates distribution groups and contacts. The group membership from on-premises groups is recreated for the corresponding cloud-based group. If an on-premises mailbox fails to be migrated, that user can't be added to a cloud-based distribution group. When that mailbox is successfully migrated in a subsequent migration, the user will be added to the group.
     
   • It migrates mailbox data, which includes email messages, contacts and calendar items, to the new cloud-based mailboxes. This is called initial synchronisation.
     
3. After the initial synchronisation process and mailboxes are successfully provisioned and migrated, the mailboxes in the on-premises Exchange organisation and the corresponding cloud-based mailboxes are synchronised every 24 hours. This is called incremental synchronisation. This means that any new messages sent to the mailboxes on the Exchange server are copied to the corresponding cloud-based mailboxes. Incremental synchronisation continues until the administrator completes the overall migration.
   Note   During incremental synchronisation, deletions made in an on-premises mailbox are synchronised to the corresponding cloud-based mailbox. This means that if a user deletes an item from the on-premises mailbox that was previously migrated to the cloud, it will be deleted from the cloud-based mailbox.
   
4. When the migration has finished running, Microsoft Exchange sends a status email message to the administrator. A migration is done when all migration requests are either completed or failed. The status email message includes links to the following CSV files:
   
   • MigrationErrors.csv, which contains information about each mailbox that failed migration.
     
   • MigrationStatistics.csv, which contains information about the number of items migrated from each on-premises mailbox. This file also contains an auto-generated, 8-character alpha-numeric password for each mailbox that was migrated. Users are required to reset this password when they log on for the first time.
     
5. Additional migration batches are started, if necessary. The migration service will skip any on-premises mailboxes, contacts or distribution groups that have already been migrated.
   
6. After all mailboxes have been successfully migrated, the administrator updates the organisation's MX record to point to their cloud-based email organisation so that email messages are delivered directly to users' cloud-based mailboxes.
   
7. After the change to the MX record has been propagated, the administrator completes the migration process. Microsoft Exchange does the following to complete the migration:
   
   • It runs a final synchronisation for all mailboxes. After this, email sent to the on-premises mailboxes is no longer copied to cloud-based mailboxes.
     
   • It sends a final status email message after the migration is complete.
     

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Here's an overview of the staged Exchange migration process. For step-by-step instructions, see Migrate a Subset of Mailboxes to the Cloud with a Staged Exchange Migration.

1. Install and configure OLSync or DirSync for your cloud-based organisation.
   
2. Create a CSV file that contains a row for each on-premises mailbox that you want to migrate to the cloud. For more information, see Prepare a CSV File for a Staged Exchange Migration.
   
3. Start a new migration using Email Migration and select one of the following Exchange migration types:
   
   • Exchange 2007 and later versions - Automatically detect connection settings with Autodiscover
     
   • Exchange 2003 and later versions - Manually specify connection settings
     
4. After you provide the connection settings to your on-premises Exchange organisation, the migration service does the following:
   
   • Tests the connection settings to your on-premises Exchange server
     
   • Verifies that OLSync or DirSync is enabled, depending on your organisation type
     
   • Prompts you to submit a staged migration CSV file
     
   • Checks that a mail-enabled user (MEU) exists in the cloud-based email organisation for each entry in the CSV file
     
   • Converts the MEU to a mailbox
     
   • Configures mail forwarding by populating the TargetAddress property on the on-premises mailbox with the email address of the cloud-based mailbox
     
5. After it creates and configures the cloud-based mailboxes, the migration service emails a report that lists the cloud-based mailboxes that were successfully created. At this point, you can tell users to start using their new cloud-based mailbox.
   
6. The migration service then migrates email messages, contacts and calendar items from the Exchange mailboxes to the corresponding cloud-based mailboxes.
   
7. Emails a final report when the data migration is complete.
   
8. Additional migration batches and their corresponding CSV migration file are created and started, if necessary.
   
9. After all on-premises mailboxes have been successfully migrated to the cloud, you can update your organisation's MX record to point to your cloud-based email organisation so that email messages are delivered directly to users' cloud-based mailboxes.
   
10. After the change to the MX record has been propagated, you complete the migration process. The migration service does the following to complete the migration:
    
    • Cleans up any records relating to the previous migration
      
    • Checks to see if there are any MEUs in your cloud-based organisation that correspond to on-premises mailboxes that haven't been migrated to the cloud and displays a warning message
      
    • Sends a final status email message after the migration is complete
      

Here's an overview of the IMAP migration process. For step-by-step instructions, see Migrate Email from an IMAP Server to Cloud-based Mailboxes.

1. Create mailboxes in your cloud-based organisation for users. For more information, see:
   
   • Import New Exchange Online Users with a CSV File
     
   • Create a New Mailbox
     
2. Create a CSV file that contains a row for each user whose IMAP mailbox you want to migrate. For more information, see Prepare a CSV file to Migrate Email from an IMAP Server.
   
3. Start a new migration using Email Migration and select the IMAP migration type.
   
4. Configure the migration:
   
   • Configure the connection settings to the IMAP server.
     
   • Select folders in the IMAP messaging system to exclude from the migration, such as Deleted Items and Junk Mail or shared and public folders.
     
   • Submit the CSV file.
     
5. When you start the migration, Microsoft Exchange does the following:
   
   • It creates a migration request for each row in the CSV file. Each migration request contains the user name and encrypted password for the account in the IMAP messaging system.
     
   • It starts processing migration requests. This part of the process is called active mailbox migration or the initial synchronisation. For each user listed in the CSV file, messages from the IMAP mailbox are copied to the corresponding cloud-based mailbox until all the mailbox data is migrated. Microsoft Exchange processes up to N migration requests at one time, where N is the maximum number of simultaneous connections that the administrator specified for the migration.
     
   • It processes the migration requests for all the users included in the CSV file.
     
6. After the initial synchronisation process and mailboxes are successfully migrated, the mailboxes in the IMAP messaging system and the corresponding cloud-based mailboxes are synchronised every 24 hours. This is called incremental synchronisation. This means that any new messages sent to the mailboxes on the IMAP server are copied to the corresponding cloud-based mailboxes. Incremental synchronisation continues until the administrator completes the overall migration.
   Note   During incremental synchronisation, deletions made in an on-premises mailbox are synchronised to the corresponding cloud-based mailbox. This means that if a user deletes an item from the on-premises mailbox that was previously migrated to the cloud, it will be deleted from the cloud-based mailbox.
   
7. When the migration has finished running, Microsoft Exchange sends a status email message to the administrator. A migration is done when all migration requests are either completed or failed. The status email message includes links to the following CSV files:
   
   • MigrationErrors.csv, which contains information about each mailbox that failed migration. The administrator can fix these errors and resubmit a new CSV file.
     
   • MigrationStatistics.csv, which contains information about the number of items migrated from each on-premises mailbox.
     
8. Additional migration batches and their corresponding CSV migration file are created and started, if necessary.
   
9. After all mailboxes have been successfully migrated, the administrator updates the organisation's MX record to point to their cloud-based email organisation so that email messages are delivered directly to users' cloud-based mailboxes.
   
10. After the change to the MX record has been propagated, the administrator completes the migration process. Microsoft Exchange does the following to complete the migration:
    
    • It runs a final synchronisation for all mailboxes. After this, email sent to the mailbox in the IMAP messaging system is no longer copied to cloud-based mailboxes.
      
    • It sends a final status email message after the migration is complete.
      

Note   As an alternative to using an IMAP migration to migrate mailbox items to cloud mailboxes, you could use the Microsoft Exchange PST Capture tool. PST Capture lets you search for and collect PST files on computers in your on-premises organisation and then import the PST files to cloud mailboxes. Note that you can also use PST Capture to import PST files to on-premises primary or archive mailboxes. For more information, see Microsoft Exchange PST Capture.

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If you’re running Office 365 for enterprises and your long-term or short-term goal is to maintain mailboxes both in your on-premises organisation and in the cloud, you can deploy Exchange Online into your on-premises organisation in what is called a hybrid deployment. In a hybrid deployment, messaging functionality is seamless across the on-premises deployment and the cloud deployment. Features of a hybrid deployment include:

• Moving on-premises mailboxes to the cloud with Mailbox Replication Service (MRS)
  
• Mail routing between on-premises and cloud-based organisations
  
• Unified global address list, also called a “shared address book”
  
• Free/busy and calendar sharing between on-premises and cloud-based organisations
  
• Message tracking, MailTips and multi-mailbox search between on-premises and cloud-based organisations
  

For more information, see Exchange Hybrid Deployment and Migration with Office 365.