Migrate E-Mail from an IMAP Server to Cloud-based Mailboxes

• Before you begin
  
• Run a migration batch
  
  • What happens after you start the migration batch?
    
  • Stop a migration batch
    
  • Start additional migration batches
    
• Complete the migration
  
• Best practices
  

Before you migrate mail from an IMAP server, be sure to plan your e-mail migration carefully, especially if you're migrating lots of users. When you plan, make sure to check out Best practices.

To prepare for the migration:

• Create a cloud-based mailbox for each user that you will migrate   Before you can migrate data from a user's mailbox on the IMAP server, the user has to have a cloud-based mailbox and user ID. Here's how to create new mailboxes and user ID for each user:
  
  • Create a New Mailbox
    
  • Import New Exchange Online Users with a CSV File
    
• Obtain the FQDN for your IMAP server   You need to provide the FQDN of the IMAP server that you will migrate mailbox data from, for example, imap.contoso.edu.
  Tip   Use an IMAP client or the PING command to verify that you can use the FQDN to communicate with the IMAP server over the Internet.
  
• Configure your on-premises firewall to allow IMAP connections   You may have to open ports in your on-premises firewall so network traffic originating from the Microsoft datacenter during the migration is allowed to enter your on-premises organization. For a list of IP addresses used by Microsoft datacenters, see Exchange Online URLs and IP Address Ranges.
  
• Decide which folders you don't want to migrate from the IMAP messaging system   For example, you may not want to migrate the contents of the Deleted Items and Junk Mail, and shared or public folders.
  Important   If you're migrating e-mail from an on-premises Microsoft Exchange server, we recommend that you exclude public folders from the migration. If you don't exclude public folders, the contents of the public folders are copied to the cloud-based mailbox of every user.
  
• Prepare the CSV file   Identify the group of users whose mailboxes you want to migrate. Include these users in the CSV file that will make up the migration batch. If you have to migrate thousands of mailboxes, it's a good idea is to migrate users in several smaller batches. For example, if you have 10,000 accounts to migrate, you could run four batches with 2,500 users each, or you could divide the batches alphabetically, by user type, such as faculty, students, and alumni, by class, such as freshman, sophomore, junior, and senior, or in other ways that will help you keep track of the users you've migrated.
  Here are the required attributes for each user:
  
  • EmailAddress specifies the user ID for the user's cloud-based mailbox.
    
  • UserName specifies the user logon name for the user's mailbox on the IMAP server.
    
  • Password is the password for the user's account in the IMAP messaging system.
    
  Here's an example of the format for the CSV file. In this example, three mailboxes are migrated:
  
  Copy

  EmailAddress,UserName,Password
  terrya@contoso.edu,terry.adams,1091990
  annb@contoso.edu,ann.beebe,2111991
  chrisc@contoso.edu,chris.cannon,3281986
  

  For the UserName attribute, in addition to the user name, you can use the credentials of a super-user account or administrator account that has the rights to access all mailboxes on the IMAP server. For more information, see Prepare a CSV File to Migrate E-mail from an IMAP Server.
  Tip   Use the CSV file that you used to import new users as the starting point for CSV migration file. For example, if you import 2,000 new users to your organization in the cloud, create a CSV file to migrate mail for those same 2,000 users.
  
• Assign the super-user or administrator account permissions to access mailboxes in your Exchange organization   If you use administrator credentials in the CSV file, the account that you use must have the necessary permissions to access the on-premises mailboxes. You can assign the Full Access permission for individual mailboxes or assign the Receive As permission for a mailbox database. For more information, see the following:
  

  Exchange 2010	Allow Mailbox Access
  Exchange 2007	Use the Add-MailboxPermission cmdlet to add permissions to a mailbox How to allow mailbox access
  Exchange 2003	Microsoft Knowledge Base article 268754 - How to assign users or groups full access to other user mailboxes Microsoft Knowledge Base article 821897 - How to assign service account access to all mailboxes in Exchange Server 2003

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After you've run all your IMAP migration batches for the mailboxes you plan to migrate, you're ready to complete the migration. Follow these steps:

1. Configure your MX record to point to your cloud-based e-mail organization    Until you change your MX record, e-mail sent to users is still routed to their mailboxes in the IMAP messaging system. When a user mailbox is successfully migrated, the mailbox on the IMAP server and cloud-based mailbox are periodically synchronized until you complete the overall migration. This lets users use their cloud-based account to access e-mail sent to their IMAP mailbox. When you configure your organization's MX record to point to your cloud-based e-mail organization, all e-mail is sent directly to the cloud-based mailboxes.
   After you change the MX record and verify that all e-mail is being routed to cloud-based mailboxes, you're ready to complete the migration.
   Important   It can take from 24 to 72 hours for the updated MX record to be propagated. Wait at least 24 hours after you change the MX record before you complete the migration. Verify that mail is being routed to cloud-based mailboxes before you complete the migration.
   
2. Complete the overall migration process   Click Complete Migration in the E-Mail Migration pane. What happens when you click Complete Migration?
   
   • Microsoft Exchange runs a final synchronization for all mailboxes. After this, e-mail is no longer synchronized between mailboxes on the IMAP messaging system and cloud-based mailboxes.
     
   • Microsoft Exchange sends a final status e-mail message after the migration is complete. If there are any errors during the final synchronization process, a MigrationErrors.csv file that lists the errors is attached to this message.
     

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Here are some tips to optimize your IMAP migration:

• Increase the connection limits to your IMAP server   Many firewalls and e-mail servers have per-user limits, per-IP address limits, and overall connection limits. Before you migrate mailboxes, make sure that your firewall and IMAP server are configured to allow a large, or maximum, number of connections for the following settings:
  
  • The total number of connections to the IMAP server
    
  • The number of connections by a particular user. This is important if you use administrator credentials in the CSV migration file because all connections to the IMAP server are made by this user account.
    
  • The number of connections from a single IP address. This limit is typically enforced by the firewall or the e-mail server.
    
  If your IMAP server is running Microsoft Exchange Server 2010 or Exchange 2007, the default settings for connection limits are low. Be sure to increase these limits before you migrate e-mail. By default, Exchange 2003 doesn't limit the number of connections.
  For more information, see:
  
  • Exchange 2010: View or Configure IMAP4 Properties
    
  • Exchange 2007: How to Set Connection Limits for IMAP4
    
  • Exchange 2003: How to Set Connection Limits
    
• Change the DNS Time-to-Live (TTL) setting on your MX record   Before you start migrating mailboxes, change the DNS TTL setting on your current MX record to a shorter interval, such as 3600 seconds (one hour). Then, when you change MX record to point to your cloud-based e-mail organization after all mailboxes are migrated, the updated MX record should propagate more quickly because of the shortened TTL interval.
  
• Run one or more test migration batches   Run a few small IMAP migration batches before you migrate larger numbers of users. In a test migration, you can do the following:
  
  • Verify the format of the CSV file.
    
  • Test the settings used to connect to the IMAP server
    
  • Verify you can successfully migrate e-mail using super-user credentials, if applicable.
    
  • Determine the optimal number of simultaneous connections to the IMAP server that minimize the impact on your Internet bandwidth. For more information, see Maximum Number of Connections to Your Mail Server.
    
  • Verify that folders you exclude aren't migrated to the cloud-based mailboxes.
    
  • Determine how long it takes to migrate a batch of users.
    
  Use CSV files with the same number of rows and run the batches at similar times during the day. Then compare the total running time for each test batch. This will help you estimate how long it will take to migrate all your mailboxes, how large each migration batch should be, and how many simultaneous connections to the IMAP server you should use to balance migration speed and Internet bandwidth.
  
• Create mailboxes and migrate e-mail for the same batch of users   Use the CSV file that you used to import new users as the starting point for the CSV file. For example, if you import 2,000 new users to your cloud-based e-mail organization, create a CSV file to migrate mail for those same 2,000 users. This is an effective way to organize and manage your migration from an on-premises messaging system to your cloud-based organization.
  
• Use super-user or administrator credentials in the CSV file to migrate e-mail   This method is the least disruptive and inconvenient for users, and it will help minimize synchronization errors caused when users change the password on their on-premises account. It also saves you from having to obtain or change user passwords. If you use this method, be sure to verify that the administrator account you use has the necessary permissions to access the mailboxes you are migrating.
  Tip   If you decide to use user credentials in the CSV file, consider globally changing users' passwords and then preventing users from changing their password on their on-premises account before you migrate their mailboxes. If users change their password before their mailbox is migrated to the cloud-based mailbox, the migration will fail. If they change their password after the mailbox is migrated, new e-mail sent to their mailbox on the IMAP server will not be migrated to their cloud-based mailbox.
  
• Don't delete mailboxes or change their SMTP addresses during migration   The migration system will report an error when it can't find a mailbox that's been migrated. Be sure to complete the migration before you delete or change the SMTP address of a cloud-based or on-premises mailbox that's been migrated.
  
• Communicate with your users   Give users a heads-up that you are migrating the content of their on-premises mailboxes to your cloud-based organization. Consider the following:
  
  • Tell users that e-mail messages larger than 35 MB won't be migrated. Ask users to save very large messages and attachments to their local computer or to a removable USB drive.
    
  • Ask users to delete old or unnecessary e-mail messages from the on-premises mailbox before migration. This helps reduce the amount of data that has to be migrated and can help reduce the overall migration time. Or you can clean up their mailboxes yourself.
    
  • Suggest that users to back up their Inbox.
    
  • Tell users which folders won't be migrated.
    
  • Folders with a forward slash ( / ) in the folder name aren't migrated. If users want to migrate folders that contain forward slashes in their names, they have to rename the folders or replace the forward slashes with a different character, such as an underscore character ( _ ) or a dash ( - ).
    
  • Tell users when they can use their cloud-based account to access the e-mail that was migrated from their on-premises account. Don't give users access to their cloud-based accounts until you're ready to complete the migration.
    Need a good way to provide users with information about their new cloud-based accounts? See Send a Welcome Message to New Users.
    

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