Email Migration

Fix Outlook.com to Microsoft 365 IMAP Migration Authentication Failed

Maira Mehtab Sep 22, 2026 868 views

Question details

The user is encountering an ImapAuthenticationException error while attempting to migrate emails from Outlook.com to Microsoft 365, despite having IMAP enabled and verifying endpoint connectivity.

Product: Microsoft 365
Device & OS: not provided
Scenario: Migrating email data from an Outlook.com account into a Microsoft 365 environment using an IMAP migration batch.
Observed behavior: The IMAP migration fails repeatedly with an ImapAuthenticationException error during the authentication phase.

Before you start

Ensure you have administrative access to the destination Microsoft 365 admin center and can log into the source Outlook.com account to manage security settings.

Solution 1Recommended

Configure Modern Authentication and App Passwords

Use this method to bypass authentication blocks caused by strict security defaults or two-step verification on the source Outlook.com account.

Modern email providers often block basic authentication requests. To allow the migration endpoint to connect successfully, you must ensure modern authentication (OAuth2) is supported or utilize a dedicated App Password if two-step verification is active.

Enable Two-Step Verification

Log in to the Outlook.com account's security dashboard. Navigate to Advanced Security Options and turn on two-step verification if it is not already enabled.

Generate an App Password

In the same Advanced Security Options menu, scroll down to the App passwords section and click 'Create a new app password'. Note the generated password securely.

Update Migration Endpoint

Go to the Microsoft 365 Exchange admin center. Edit your IMAP migration endpoint settings and replace the standard Outlook.com account password with the newly generated app password.

Resume Migration Batch

Save the endpoint configuration and resume the IMAP migration batch to verify if the authentication succeeds.

OAuth2 Requirement: If your migration tool specifically requires OAuth2, ensure you are selecting the modern authentication method in the migration setup wizard rather than basic IMAP auth.

Solution 2

Consult Microsoft Exchange Support

If configuration updates and app passwords do not resolve the issue, seek specialized assistance from Microsoft's Exchange community.

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Frequently Asked Questions

Why do I get an ImapAuthenticationException when IMAP is definitely enabled?

This exception usually occurs because basic authentication is blocked by Microsoft's modern security defaults. Even if IMAP is enabled, the server rejects the connection unless you use Modern Authentication (OAuth2) or an app password.

How do I generate an app password for Outlook.com?

Go to your Microsoft account security settings, select 'Advanced security options', ensure two-step verification is turned on, and then select 'Create a new app password' under the App passwords section.

Can I migrate Outlook.com to Microsoft 365 without enabling two-step verification?

It is increasingly difficult due to mandatory modern security policies. Microsoft highly recommends enabling two-step verification and using an app password for IMAP connections to ensure a secure and successful migration.

Migration & Recovery