Questions: How to migrate mail to M365 using IMAP migration?

As for IMAP migration to M365 using one password, you can migrate the contents of user mailboxes from your source email system to Microsoft 365 or Office 3653. If you know the user passwords or can access their mailboxes by using administrator credentials, there won’t be any impact to users until you shut down your source email system4. If you can’t access user mailboxes, you’ll have to reset the passwords4. This lets you access the user mailboxes by using a new password that you know4.

When you create a migration file in this task, you type your mailbox admin credentials and usernames using a special format. This allows you to access user mailboxes without knowing or resetting the user passwords3. We provide the format used by Exchange, Dovecot, and Mirapoint IMAP servers3.

Here is an example of what the CSV file might look like:

EmailAddress,UserName,Password
usera@contoso.com,#usera@contoso.com#admin#,AdminPassword
userb@contoso.com,#userb@contoso.com#admin#,AdminPassword

In this example, usera@contoso.com and userb@contoso.com are the email addresses of the users you’re migrating. #usera@contoso.com#admin# and #userb@contoso.com#admin# are the usernames in the special format, where admin is the administrator usernameAdminPassword is the password for the administrator account3.

Please note that this is a general example and the exact format may vary depending on the source email system. Always refer to the specific documentation or support for your source email system for the most accurate information. Also, remember to handle all sensitive information, such as passwords, with care to ensure data security.

https://video2.skills-academy.com/en-us/exchange/mailbox-migration/migrating-imap-mailboxes/migrate-other-types-of-imap-mailboxes