Microsoft Office Tutorials and References
In Depth Information
An IMAP migration is commonly used in migrations from non-Exchange email systems to
Exchange Online. As the name implies, the on-premises email system will need to have
the IMAP protocol enabled to use an IMAP migration method. Prior to initiating an IMAP
migration, there are two manual tasks you must perform:
● Create the Exchange Online mailboxes for users whose mailbox contents you want to
● Create a .csv file with the email address, user name, and password for each mailbox
you will be migrating.
Like cutover and staged migrations, you will use either the ECP or EAC GUI to initiate an
IMAP batch migration. You can also use Windows PowerShell to initiate an IMAP batch
Creating a .csv file
Create a .csv file to target the on-premises users’ mailboxes whose content you want to
migrate to Exchange Online. The first row of the .csv file is the header row and should
contain only the following attribute names:
EmailAddress This is the user ID for the user’s cloud-based mailbox in UPN format.
Note that this is not the SMTP address; this is the user ID in Office 365.
UserName This is the user logon name for the on-premises mailbox on the IMAP
Password This is the password for the user’s account on the on-premises IMAP
The .csv file for an IMAP migration batch must not be larger than 10 MB and cannot
contain more than 50,000 rows. Furthermore, all three attributes are required. Contacts,
calendar items, and tasks cannot be migrated with the IMAP method.
IMAP migration with the ECP
Follow these steps if your organization has not been upgraded to the latest release of
Office 365 and would like to use the ECP to initiate an IMAP migration. This section
assumes you have created mailboxes in Exchange Online for the on-premises users for
whom you want to migrate content.
1. Log on to OWA.