On-Premises Exchange 2003 to Microsoft 365 Migration Guide

This article will guide you through the steps for migrating mailboxes from On-Premises Exchange 2003 servers to Microsoft 365. This task flow will not work for Exchange 2007+ or Hosted Exchange. For those workflows, refer to the Exchange Migration Guides list.

There are some tools and resources that will make the migration easier.


MigrationWiz is a migration tool, not a syncing tool. If changes are made at the source after migration, they will not sync to the destination, nor will changes made at the destination sync to the source. We do not have “live” monitoring of changes (as with a sync agent) and we cannot handle scenarios such as conflict resolution without user interaction.

MigrationWiz supports the capability to share migration projects across a Workgroup. When the Project Sharing feature is turned on, all Agents besides those who are Inactive can view all migrations projects. 

First Migration?

We have created a guide on scoping, planning, and managing the migration process for your use. If this is your first migration, we recommend reading this guide carefully.


Please consider the information below before choosing this migration type.


We recommend that you purchase User Migration Bundle licenses for this migration scenario. User Migration Bundle licenses allow the performance of multiple migrations with a single license. For questions on licensing, visit MigrationWiz Licenses.

Use your license by following the next steps:

  1. Purchase Licenses.
  2. Create a Customer.
  3. Apply Licenses.
  4. Review Considerations.
Purchase Licenses Create a Customer Apply Licenses Considerations

Purchase licenses by following the steps below:

  1. Sign in to your BitTitan account. 
  2. In the top navigation bar, click Purchase.
  3. Click the Select button and choose User Migration Bundle licenses.
  4. Enter the number of licenses you want to purchase. Click Buy Now.
  5. Enter a Billing address if applicable.
  6. Click Next.
  7. Review the Order Summary and enter a payment method.
  8. Click Place Your Order.


Please consider the following limitations when performing a migration.

  • We are not able to support migrations with two-factor or multifactor authentication. 
  • The maximum size of individual files that can be migrated is 60GB.
  • App passwords are not supported for the Microsoft 365 endpoint. 
What items are and are not migrated?

Migrated items vary by version of Exchange. The following list is for Exchange Server 2003. If you are using an alternate version of Exchange, please refer to the Migrated and Not Migrated Items list and check for your version of Exchange.

Exchange Server 2003


  • Inbox
  • Folders
  • Email
  • Contacts
  • Calendars
  • Tasks
  • Journals
  • Notes
  • Post (when the destination is Exchange or Microsoft 365)

Not Migrated

  • Inactive inboxes
  • Email templates
  • Email flags (if the destination is G Suite)
  • Safe Sender/Block Lists
  • Mail Settings
  • Standalone documents stored in Mailbox Folders or Public Folders (Example: IPM.Document item types)
  • System Public Folders
  • StickyNote folders
  • Public Folders
  • BCC recipients on email items 
  • Optional attendees of calendar entries (Microsoft Exchange Web DAV API does not return this information for items)


Before submitting a migration, please consider the following information regarding Calendar Permissions migration from Exchange as the source:

Calendar Permissions can be migrated except for Resource Calendars, only if an account exists at the destination that matches the UPN prefix of an account with Calendar Permissions at the source. Otherwise, if there is no matching account at the destination, Calendar Permissions will not be migrated.

Exchange questions and troubleshooting

Our Exchange Mailbox FAQExchange Migration Setup and Planning, and Exchange Mailbox Migration Troubleshooting guides contain many common questions and concerns, along with more information, guidance, and steps to resolve issues such as throttling.

Prepare the Source Environment

Set Up Admin Account

To create an administrator account (e.g., MigrationWiz), perform the following steps when logged into the Exchange Server.

  1. Open the System Manager.
  2. Expand the Recipient Configuration node.
  3. Right-click on the Mailbox node.
  4. Click on New Mailbox.
  5. Click on Next.
  6. Click on Next.
  7. Enter "MigrationWiz" as the first name.
  8. Enter "MigrationWiz" as the user logon name, and optionally select a user principal name (UPN) domain.
  9. Enter a password and confirm the password.
  10. Click on Next.
  11. Click on Browse to select a Mailbox database.
  12. Click on Next.
  13. Click on New.
  14. Click on Finish.


If you have not already done so, set up router ports for OWA traffic, by following the steps in the Prerequisites section of this article. Set different OWA URLs for each environment and configure router ports to accept inbound/outbound mail traffic for those OWA URLs.

If you have followed through all the prerequisite steps of this guide, this step will already have been completed.

Test Mailbox Access

To test mailbox access on the Exchange Server 2003, perform the following: 

  1. Open the browser to https://mail.example.com/exchange  
    • Ideally, we recommend opening this URL from a non-domain-joined machine on a different network than the Exchange Server. 
    • com is the DNS name of the OWA server. 
  2. When prompted for credentials, enter the username and password of the account to be used to access the mailbox. 
    • This can be either the credentials of the end user mailbox itself or administrative credentials.
    • To migrate using administrative credentials, enter administrative credentials into OWA. 
    • The Inbox of the end user's mailbox or administrator's mailbox should be visible once logged in. 
  3. If using administrative credentials, change the URL to  https://mail.example.com/exchange/user@example.com
    • user@example.com is the primary SMTP address of the mailbox being accessed. 
    • The result is that the Inbox of the mailbox user@example.com should be visible. 

Configure the Exchange Authentication Method

To configure the Exchange authentication method:

  1. Open the Exchange System Manager.
  2. Expand the Server node.
  3. Expand the server node.
  4. Expand the Protocols node.
  5. Expand the HTTP node.
  6. Expand the Exchange Virtual Server node.
  7. Right-click on the Exchange node and select Properties.
  8. Click on the Access tab.
  9. Click on the Authentication button.
  10. Make sure Basic Authentication is selected as the only authentication mode, and a single backslash (\) is specified for the Default domain.
  11. Click on OK.
  12. Click on OK.
  13. For the Public node, repeat Steps 7-12​.

Make sure that the settings are identical in IIS:

  1. Open the Internet Information Services (IIS) Manager.
  2. Expand your server.
  3. Expand the Web Sites node.
  4. Expand the Default Web Site node (or website node that contains your Exchange virtual directories).
  5. Right-click on Exchange in the navigation tree on the left, and select Properties.
  6. Click the Directory Security tab.
  7. Click the Edit button within the Authentication and Access Control section.
  8. Make sure Basic Authentication is selected as the only authentication mode, and a single backslash (\) is specified for the Default domain.
  9. Click on OK.
  10. Click on OK.
  11. For the Public node, repeat Steps 5-10.

Make sure to back out any .config file so that you can easily go back to the previous state.

Increase MAPI-named Property Limits

  1. Start the Registry Editor on the mailbox server.
  2. Locate the following registry key:
    • HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<ServerName>\<Private-GUID>
  3. Set the following DWORD values or create new values if they do not exist.
    • NonMAPI Named Props Quota == 00007fff
    • Named Props Quota == 00007fff

You may either wait approximately 30 minutes for these values to take effect automatically, or reboot the server to take effect immediately.

These instructions have also been documented on the Microsoft website.

Prepare the Destination Environment

Create an Admin Account

  1. Create a user in Microsoft 365.
  2. Connect to Exchange Online by using remote PowerShell.
  3. Type the following command, and then press Enter:
    Get-Mailbox -ResultSize unlimited -Filter {(RecipientTypeDetails -eq 'UserMailbox') -and (Alias -ne 'Admin')} | Add-MailboxPermission -User AdministratorAccount@mydomain.com -AccessRights fullaccess -InheritanceType all

After you perform these steps, the specified user will be able to access all user mailboxes in Microsoft 365. The user will be able to view the contents of the mailboxes from either Outlook or Outlook Web App.

Set Up Accounts in Microsoft 365

Set up accounts on Microsoft 365 and assign licenses. These can be created in several ways:

Prepare the Tenant to Send & Receive Large Items

We do not impose any limit on item/attachment sizes. However, large items/attachments can fail to migrate because of external factors.  There are two considerations:​

  1. What is the maximum attachment size allowed by the Destination system? 
    • Most email systems impose size limits. For example, if the Destination system has a 30MB limit, any item/attachment larger than 30MB will fail to migrate.
  2. What is the connection timeout for the Source and Destination system? 
    • ​​For security reasons, most email systems close opened connections after a predetermined amount of time. For example, if the Destination system only has 512Kbps of network bandwidth and closes connections after 30 seconds, we may be unable to transfer large items/attachments before the connection is closed.

MigrationWiz will automatically make multiple attempts to migrate large items. Upon completion of a migration, you may resubmit it in error retry mode to try to migrate failed items. This is always free of charge.:

When migrating from or to Office 365 use the steps provided here to increase the Max Send and Max Recieve quotas, Change message size limits in Office 365.

Modern Authentication Requirements

The steps listed in the Obtain Client and Tenant ID Settings for Mailbox and Exchange Online Migrations section of the Authentication Methods Migrations KB apply to both the source and destination tenant when they are Exchange Online, in regards to Exchange Web Services (EWS) in mailbox, archive mailbox, and public folder projects. Use a Global Administrator for the configuration steps.

Please review the documentation before preparing the destination.

Updated Mailbox Permission Steps to Use in Place of the Application Impersonation Role

Starting in May 2024, Microsoft announced that they will begin blocking the assignment of the Application Impersonation role in Exchange Online and that in February 2025, they will completely remove this role and its feature set from Exchange Online, for more information click here.

If you do not already have an admin account with the Application Impersonation role assigned, use the steps outlined in the following KB to add the necessary API permissions (to use in place of the Application Impersonation role) to the Modern Authentication app you are using for your O365 mailbox or archive mailbox endpoint.

MigrationWiz Steps

Create a Mailbox Migration project

  1. Click the Go to My Projects button.
  2. Click the Create Project button.
  3. Click on the type of project that you wish to create. For this migration:
    • Mailbox: Mailbox projects are used to migrate the contents of the primary user mailbox from the previous environment to the new environment. Most mailbox migrations can migrate email, calendars, and contacts.


      For mailbox migrations, use administrative credentials to access mailboxes. In most migration scenarios, the admin account needs to have full access rights to the Source mailboxes.
  4. Click Next Step.
  5. Enter a Project name and select a Customer.
  6. Click Next Step.
  7. Select or create a source endpoint.
  8. Select or create a destination endpoint.
  9. Click Next Step.
  10. Click Save and Go to Summary.


Endpoints are now created through MigrationWiz, rather than through MSPComplete. The steps for this section outline how to create the endpoints in MigrationWiz.


If you select an existing endpoint, keep in mind that the drop-down only shows ten endpoints. If you have more than ten, you may need to search.
Endpoint search is case and character-specific. For example, Cust0mer will not show up if the search is customer. We recommend keeping a list of endpoints you have created, along with any unique spellings or capitalization you may have used. 

Client Secret for Microsoft 365 Endpoints

For all Microsoft 365 Endpoints mailbox migrations (including archive migrations), MigrationWiz adds the Client Secret field, which is not always mandatory. It will depend on the permissions of the user account that performs the migration. Please review the following information before the creation of your M365 endpoints.

  • The client secret value is not mandatory if you use delegated permissions. Please leave the Client Secret field empty.

  • The client secret value is mandatory if you use the RBAC approach for application impersonation.

  • If you already have an admin account with the Impersonation role enabled (not using the RBAC approach) the client secret value is not mandatory. Please leave the Client Secret field empty.

Create a Source Endpoint

  1. Click New.
  2. Name your endpoint.
  3. Select type Exchange Server 2003+.
  4. Enter the OWA URL.
  5. Provide credentials: Click the Provide Credentials radio button, and enter the admin account credentials for the account, previously set up under the Prepare the Source Environment section of this guide.
  6. Click Add.

Create a Destination Endpoint

  1. Click New.
  2. Name your endpoint.
  3. Select type Office 365.
  4. Provide the credentials.
  5. Click Add.
  6. Complete the Application (client) ID, the Directory (tenant) ID, and the Client Secret fields.Destintation Settings.png


    Do not forget to complete the client ID, and the tenant ID fields, otherwise, you cannot save your project migration.

Once the information has been provided for both, the source and/or destination endpoint, and the customer selects Save and Go to Summary, MigrationWiz performs an endpoint validation check for the Microsoft 365 endpoint.

This validation tests the administrator credentials entered into the project and the Modern Authentication setup only. If there is an issue, the screen redirects to the endpoint and provides an error message or flyout that can be selected for more information regarding the error.

Common Errors when Configuring Your Endpoint

For more information, review the AADSTS700016, AADSTS90002, and ADDSTS50126 issues on the Common Errors Using Modern Authentication page.

Add Users

Add the user accounts that will be migrated to the project. MigrationWiz allows you to bulk import mailboxes into the system. Bulk Add uses a CSV containing the source and destination email addresses for the users to add the users to the project.

To import one or more mailboxes:

  1. Sign in to your MigrationWiz account.
  2. Select the Project for which you want to perform the bulk import.
  3. Click Add.
  4. Click Bulk Add.
  5. Follow the instructions on the page.

Advanced Options

The following advanced options may be useful for your migration. 

Support Tab

Default Options for Microsoft 365 Endpoints

By default, some fields are view-only. In other words, you cannot edit or remove them from the support options page. To edit them, you need to edit the source or destination endpoint of your project.

Among these default options, you can find ModernAuthClientIdExport, ModernAuthTenantIdExport, ModernAuthClientSecretExport, ModernAuthClientIdImport, ModernAuthTenantIdImport, and ModernAuthClientSecretImport. 

The support options above are required when configuring your endpoint.


Keep in mind that the ModernAuthClientSecretExport and the ModernAuthClientSecretImport support options are text-masked.


You cannot update the default Advanced Options, in case you try to modify or add new ones the following message arises.
Duplicate Support Option.png

Source/Destination Tab

Set to use impersonation at Destination. Check the Use impersonation at Destination box. 

Run Verify Credentials

  1. ​Sign in to your MigrationWiz account​.
  2. Open the Project containing items you wish to validate.
  3. Select the items you wish to validate.
  4. Click on the Start button in your dashboard.
  5. Select Verify Credentials from the drop-down list.

Once complete, the verification results will be shown in the Status section.​ 

Notify Users

Notify users that a migration is occurring. Send an email to all users telling them the time and date of the migration.

Run Migration

Pre-Stage pass

  1. Select the users to migrate.
  2. Click the Start button from the top.
  3. Select Pre-Stage Migration.
  4. Under the Migration Scheduling section, select 90 days ago from the drop-down list.
  5. Click Start Migration.

MX Record Cutover

Change over MX records on the DNS provider's portal.

Also, include the AutoDiscover (CName) setting.

Full (Delta) pass

  1. Select the users to migrate.
  2. Click the Start button from the top.
  3. Select Full Migration.
  4. Click Start Migration.

Run Retry Errors

Look through the user list and click any red "failed migration" errors. Review the information and act accordingly.

If problems persist contact Support.

Request Statistics

Click the pie chart icon in the MigrationWiz dashboard to receive an email containing all the project migration statistics.


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