Office 365 IMAP Migration From Different Domain

Often I get asked if it is possible to perform an IMAP Migration from an e-mail system that is using a different domain than the one being used in Office 365. A typical scenario are those who want to migrate from Gmail (… into Office 365, either using a custom domain or the Microsoft-provided one (…@<domain>

Most of the times, the question comes to light when they try to perform exactly this but receive the following error message:

MigrationRecipientNotFoundExceptionMigration rate:Error: MigrationRecipientNotFoundException: A recipient wasn‎'t found for ”<user>” on the target. Create a recipient of the appropriate type for this migration on the target and try again.


It is perfectly possible to use IMAP migration to migrate users who have different e-mail address suffix other than the domain which verified in Office 365!

The reason why we get this error, is simply because the CSV file used in the migration was not created properly. As a quick overview, the CSV file can contain up to 50,000 rows, one row for each user, and can be as large as 10MB. However, it is always a good idea to migrate users in smaller batches.

The required attributes for each user are as follows:

    • EmailAddress specifies the e-mail address of the target mailbox in Exchange Online;
    • UserName specifies the user logon name for the user’s source mailbox on the IMAP server (in this example Gmail);
    • Password is the password for the user’s account in the IMAP messaging system.

The problem here is that sometimes administrators use the EmailAddress attribute to specify the e-mail address of the source mailbox, when it is actually used to match a source mailbox to its target mailbox. However, there is no need for a source e-mail address as no similar process to autodiscover is performed. Exchange will use the username and password specified, and try to connect to the source system using the connection settings for the migration batch:


As long as all these settings are correct, you should have no problems!

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