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On Demand Migration for Email Current - User Guide

Introduction Preparing Migrations Test and Pilot Migrations Configuring and Running Migrations Post Migration Third Party Assessments and Certifications Glossary

Running Migration

After you have connected to your source and target email services, imported the mailboxes you want to migrate, and optionally, selected what mailbox items to exclude from the migration, you are ready to run the migration.


Caution: Before starting a migration, be aware of the following:

Each mailbox in a source email service can be migrated successfully a total of 10 times with a maximum extraction limit of 500 GB across all migrations. This includes mailboxes that have 10 different date filters. This limit applies even if the 10 migrations do not migrate the same message more than once.



Note: Migration from Microsoft 365 to Microsoft 365

If you switch your source domain and MX record to the target domain before the migration is completed, ODME cannot connect to the source mailboxes using old SMTP addresses, and so you need to add mailbox pairs with the new source SMTP addresses to the migration plan. In this case, an additional ODME license is consumed for each newly added mailbox pair except the following scenario:

  1. Migration session N: --> or any other user's target SMTP address
  2. "" domain name is transferred to the target.
  3. Migration session N+1: or any other user's source SMTP address -->

In this scenario, an extra-license will not be consumed on the step 3 despite the change of the source user SMTP address.

To run a migration:

  1. Open the Dashboard and select the migration plan you want to run.
  2. Open the Migrate tab.

The Migrate tab lists all the mailboxes that have been imported (up to 5000).

  1. Optionally, make any changes to the migration settings as summarized in the in Dashboard or in the Migration Checklist of the Migrate tab.

The migration plans in the Dashboard and the Migration Checklist in the Migrate tab display links pointing to the Connections, Mailboxes and Options tabs. Click a link to return to the tab and make the changes you want.


Note: The Migration Checklist displays the IP addresses of the ODME web services used to run the migration (which are distinct from the web services used to validate connections to the source and target email services). The system administrator should verify that no firewall rules exist that will prevent the ODME web services identified by the IP addresses from running a migration.

  1. Click Start Migration.

During the migration, each mailbox displays what percentage of the mailbox has been migrated. At the bottom a colored progress bar indicates the overall status of the migration.

When the migration is complete, the number of mailboxes that were successfully migrated and the number that were interrupted or failed to migrate are displayed in the Migration Status section

For each mailbox, ODME also displays:

  • The number of errors encountered during the migration


Note: The number of errors reported for a mailbox's migration displayed in the Migrate tab may be lower than the number of error messages reported in the mailbox's migration logs. This is because certain errors counted in a mailbox's migration may be the result of several related errors reported in the migration logs. For example, ODME may fail to migrate a mailbox item for a combination of reasons, each one resulting in a separate error reported in the migration log. For the mailbox's migration, however, this failure is counted as one error.

  • The estimated number of items (messages, contacts, distribution lists, appointments, and tasks) the mailbox contains
  • The total number of mailbox items that were successfully migrated as well as the percentage (a successful migration is where 90% or more of the items migrated)


Note: For migrations from a G Suite source, the Migration Status section indicates whether ODME has paused data extraction from Google due to hitting the data extraction limit or because Google throttled the connections. The Mailbox column shows when the migration will be restarted. There is also a tooltip to the right of the 'auto-resume' message explaining why the migration has been paused and that it will resume after 24 hours.

  1. Optionally, to view migration log entries for a single mailbox, click the View Log link for that mailbox.


Note: For migrations from a G Suite source, log messages indicate whether ODME paused its data download from Google. The messages indicate why ODME is pausing, how many items (contacts, calendar and email) ODME has migrated so far, and when ODME will re-start the migration. The messages also indicate if ODME paused due to hitting the data extraction limit or because Google throttled the connections.

  1. If some issues or unexpected errors occurred during the mailbox migration, the mailbox will be marked as "Interrupted" or "Failed". To restart the migration process for one or several "Interrupted" or "Failed" mailboxes, you can select the checkbox next to the mailbox and click the Restart Selected button.

Migration Concurrency

Though the number of mailboxes that can be migrated by the product concurrently is virtually unlimited, during migration process you can encounter some limitations outside the product.

In some cases, your source or target environment may not be able to keep up too many mailboxes being migrated simultaneously while still being responsive and available to their users. To avoid this problem you can limit the number of mailboxes migrated concurrently in a migration plan. Please see Limiting Concurrent Migrations for details.

Another limit you can hit is the maximum number of PowerShell connections. The product uses PowerShell to configure the forwarding options (Forwarding new items as they arrive and Turn off existing forwarding) for Exchange / Microsoft 365. If a migration plan has one or more of these options enabled for Exchange / Microsoft 365, when it starts, it opens a PowerShell connection to configure the enabled options. If you have too many plans configured under the same administrative account and they start approximately at the same time, you can hit the ‘PowerShellMaxConcurrency’ throttling limit for this account. In this case, the plan hit that limit will be rescheduled to start later, when a PowerShell connection is available, and the corresponding message will be displayed in the plan. Please consider to specify a different administrative account for paused plans if you need them to start immediately. Note that the connections under the same account may be done outside the product.


If you rerun a migration from Exchange 2010, 2013, 2016, 2019 or Microsoft 365, On Demand Migration for Email re-migrates mail, calendar, contact, task, and sticky note items that have changed in the source mailbox to the target mailbox. Also, calendar items that have been removed from the source mailbox will be removed from the target mailbox.

Post Migration


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