Exchange Online Migration Logs Explained
Migration logs are diagnostic records generated during mailbox migrations that capture the status, progress, and outcome of each migration operation. They provide administrators with detailed information about mailbox processing, synchronised items, skipped items, warnings, errors, and overall migration health. Whether migrating from Exchange Server, another Microsoft 365 tenant, or a third-party messaging platform, migration logs are an essential source of information for validating migration results and troubleshooting issues.
Unlike the overall migration status displayed in the Exchange Admin Centre (EAC), migration logs provide mailbox-level details that help administrators determine why a migration succeeded, completed with warnings, or failed. These logs include timestamps, synchronisation statistics, data consistency information, skipped items, and error messages that can be correlated with Exchange Online events to identify the root cause of migration issues. Microsoft recommends reviewing migration reports and migration user statistics throughout the migration lifecycle rather than relying solely on the batch status.
When planning or validating mailbox migrations using EdbMails Office 365 Migration Software, administrators should review migration logs after every migration batch to verify successful mailbox processing, identify failures, and confirm data integrity before completing the migration project.
What Are Exchange Online Migration Logs?
Exchange Online migration logs are detailed reports generated by the Exchange migration service during mailbox migration operations. These reports record the activities performed for each migration batch and individual mailbox, enabling administrators to monitor progress, investigate failures, and verify successful data transfer.
Depending on the migration type, logs may be generated for:
- Remote move (Hybrid) migrations.
- Cutover migrations.
- Staged migrations.
- IMAP migrations.
- Public folder migrations.
- Cross-tenant mailbox migrations.
- Third-party migration projects using Exchange Online as the destination.
Migration logs typically record mailbox identity, migration status, synchronisation progress, number of migrated items, skipped items, data consistency information, migration timestamps, warning messages, error details, retry attempts, and completion status.
In Exchange Online, migration statistics are maintained for both migration batches and individual migration users. Administrators can review these statistics in the Exchange Admin Centre or retrieve detailed information using Exchange Online PowerShell cmdlets such as Get-MigrationUser, Get-MigrationUserStatistics, and, for mailbox moves, Get-MoveRequestStatistics.
Why Migration Logs Are Important
Migration logs serve as the primary diagnostic resource for validating mailbox migrations and identifying issues that may not be visible from the overall migration status. Even when a migration batch reports a successful completion, individual mailboxes may contain skipped items, warnings, or transient errors that require administrator review.
Troubleshooting Migration Failures
Migration logs provide detailed error information that helps administrators determine why a mailbox failed to migrate. Common issues such as authentication failures, endpoint connectivity problems, mailbox corruption, or permission errors are typically recorded in the migration report, making it easier to identify the affected mailbox and the stage at which the failure occurred.
Validating Mailbox Integrity
Successful completion of a migration does not always indicate that every mailbox item was transferred. Migration logs include statistics for synchronised items, skipped items, and warnings, allowing administrators to confirm that mailbox data has been migrated within acceptable limits. Exchange Online also evaluates migration quality using the Data Consistency Score, which classifies migrations based on detected inconsistencies and indicates whether administrator review or approval is required.
Performance Analysis
Migration logs record processing times, synchronisation duration, and migration progress for each mailbox. Reviewing these values helps administrators identify unusually slow mailboxes, network bottlenecks, or service throttling that may affect overall migration performance. Performance analysis is particularly valuable during large-scale enterprise migrations where thousands of mailboxes are processed across multiple migration batches.
Audit and Operational Verification
Migration logs provide an operational record of mailbox processing activities. Administrators can use these records to verify that migration batches completed as planned, determine when specific mailboxes were processed, and document migration outcomes for internal change management or post-migration validation. Although migration logs are not intended to replace organisational auditing or compliance solutions, they provide valuable operational evidence during migration projects.
Types of Migration Logs
Exchange Online generates different types of migration reports depending on the migration method and the services involved. Understanding the purpose of each report helps administrators locate relevant troubleshooting information more efficiently.
Migration Batch Logs
Migration batch logs summarize the overall progress of a migration batch. They include information such as batch status, the number of mailboxes being processed, synchronization progress, completion status, and any batch-level warnings or errors. Administrators typically review batch logs first to determine whether a migration completed successfully before investigating mailbox-specific issues.
Migration User Statistics
Migration user statistics provide detailed information for individual mailboxes within a migration batch. These reports include mailbox status, items synchronised, items skipped, timestamps, migration duration, warnings, and detailed error messages. Because mailbox-specific issues are often hidden within an otherwise successful migration batch, migration user statistics are one of the most valuable resources for troubleshooting Exchange Online migrations.
Move Request Reports
Hybrid and remote move migrations generate move request reports through the Mailbox Replication Service (MRS). These reports track mailbox movement between Exchange Server and Exchange Online, including synchronisation stages, move request status, retry attempts, and completion details. Administrators can retrieve move request information by using Exchange Online PowerShell cmdlets such as Get-MoveRequest and Get-MoveRequestStatistics, which provide detailed diagnostic information for each mailbox move.
Where to Find Exchange Online Migration Logs
Exchange Online provides multiple interfaces for accessing migration logs and diagnostic reports. The level of detail available depends on whether you are reviewing a migration batch, an individual mailbox, or a mailbox move performed by the Mailbox Replication Service (MRS). Using the appropriate reporting interface helps administrators identify migration failures more efficiently and verify mailbox processing.
Exchange Admin Centre (EAC)
The Exchange Admin Centre (EAC) is the primary interface for monitoring Exchange Online mailbox migrations. Under Migration, administrators can view all migration batches, monitor their status, and access detailed reports for individual mailboxes.
Migration reports available through the EAC include:
- Migration batch status
- Number of synchronised mailboxes
- Completed and failed mailbox counts
- Individual mailbox migration status
- Warning and error messages
- Synchronization progress
- Migration start and completion times
Mailbox-level reports are particularly useful because they identify mailboxes that were completed with warnings or encountered transient failures, even when the overall migration batch reports a successful status.
Exchange Online PowerShell
For large-scale or automated migration projects, Exchange Online PowerShell provides more detailed diagnostic information than the graphical interface.
Common cmdlets include:
Cmdlet Purpose Get-MigrationBatch Displays migration batch information and current status. Get-MigrationUser Lists mailboxes associated with a migration batch. Get-MigrationUserStatistics Retrieves detailed migration statistics for individual mailboxes. Get-MoveRequest Displays active mailbox move requests. Get-MoveRequestStatistics Provides detailed mailbox move diagnostics for hybrid and remote move migrations. These cmdlets expose additional properties that may not be visible in the Exchange Admin Centre, including synchronisation state, mailbox move progress, retry history, and detailed error information.
Migration Reports
Migration reports consolidate diagnostic information collected during mailbox processing and provide administrators with a chronological record of migration events.
Depending on the migration type, reports may include:
- Migration phase progression
- Connection validation
- Mailbox synchronisation status
- Item processing statistics
- Skipped item summaries
- Retry attempts
- Warning messages
- Failure descriptions
- Completion confirmation
Administrators should review these reports after every migration batch to confirm that mailbox synchronisation completed successfully before proceeding with additional migration activities.
Understanding Common Log Entries
Migration logs contain numerous fields that describe mailbox processing, synchronisation progress, and migration outcomes. Understanding these entries helps administrators interpret migration reports more effectively.
Mailbox Identity
Identifies the mailbox currently being processed. This field typically contains the mailbox alias, User Principal Name (UPN), or primary SMTP address and enables administrators to correlate reported issues with specific users.
Migration Status
Indicates the current processing state of the mailbox.
Common status values include:
- Queued
- Syncing
- Synced
- Incremental Sync
- Completed
- Completed with Warnings
- Failed
- Removing
A mailbox reported as Completed with Warnings should always be reviewed to determine whether skipped items or recoverable errors require further action.
Items Migrated
Displays the number of successfully synchronized mailbox items. This value provides an indication of migration progress and helps verify that mailbox content has been transferred to the destination.
Skipped Items
Lists mailbox items that could not be migrated because of corruption, unsupported properties, damaged attachments, or other validation failures. A small number of skipped items may be acceptable depending on organizational policies, but administrators should investigate recurring or unusually high skip counts.
Failed Items
Represents mailbox items that could not be processed successfully and require administrator review. Unlike skipped items, failed items often indicate conditions that interrupted the migration process or prevented successful synchronisation.
Start Time and Completion Time
These timestamps record when mailbox processing began and when synchronisation completed.
Reviewing timestamps helps administrators:
- Estimate migration duration.
- Identify processing delays.
- Correlate migration events with service incidents or network interruptions.
- Measure migration throughput across multiple batches.
Completion Percentage
Indicates the proportion of mailbox data that has been synchronized. During active migrations, this value helps administrators estimate remaining processing time and identify mailboxes progressing more slowly than expected.
Warnings
Warnings identify recoverable conditions that did not stop the migration but may require administrative review.
Examples include:
- Skipped corrupted items
- Retried synchronization operations
- Temporary throttling events
- Minor folder inconsistencies
Although warnings do not necessarily indicate migration failure, they should be reviewed before completing the migration project.
Error Details
Error entries contain diagnostic information describing why a mailbox or mailbox item failed to migrate.
Typical information includes:
- Error description
- Failure category
- Affected mailbox
- Processing stage
- Retry attempts
- Recommended remediation (where available)
Administrators should always investigate the first reported error because subsequent errors are frequently secondary effects of the original failure.
Common Migration Errors Found in Logs
The following issues are among the most frequently encountered during Exchange Online mailbox migrations.
Issue How it appears in migration logs Recommended troubleshooting approach Authentication failure Authentication failed, unauthorised access, or credential validation errors Verify Modern Authentication, administrative credentials, Conditional Access policies, and Multi-Factor Authentication requirements. Mailbox locked or unavailable Mailbox unavailable, mailbox locked, or mailbox being processed Wait for mailbox operations to complete and retry the migration after verifying mailbox availability. Large item failures Large item skipped or maximum item size exceeded Review mailbox item size limits and determine whether skipped large items require manual remediation. Corrupted mailbox items Corrupt item detected, unreadable message, or invalid mailbox object Review skipped items and rerun the migration if necessary. Repair corrupted mailbox data before another migration attempt when applicable. Exchange Online throttling Request throttled, server busy, or temporary service limitation Reduce concurrent migration batches, allow retry operations to complete, and schedule migrations during periods of lower activity. Permission-related failures Access denied or insufficient permissions Confirm Exchange administrative roles and verify that the migration account has permission to access both the source and destination mailboxes. Endpoint connectivity failures Unable to connect to migration endpoint or service unavailable Validate migration endpoint configuration, network connectivity, DNS resolution, firewall rules, and Exchange Online service availability. Duplicate or unresolved mailbox objects Mailbox already exists, duplicate recipient, or recipient not found Verify Microsoft Entra ID synchronisation, recipient uniqueness, and mailbox mapping before restarting the migration. Understanding these error patterns enables administrators to distinguish between transient service conditions and configuration issues that require corrective action before rerunning the migration.
How to Analyse Migration Logs
Reviewing migration logs systematically helps administrators identify the root cause of migration issues without relying solely on the overall migration status. A structured approach also reduces the time required to troubleshoot failed or partially completed mailbox migrations.
Step 1: Verify the Migration Batch Status
Begin by reviewing the migration batch to determine its overall status. A batch may report Completed, Completed with Warnings, Syncing, or Failed. Although a completed batch indicates that mailbox processing has finished, it does not guarantee that every mailbox or mailbox item was migrated successfully. If the batch reports warnings or failures, identify the affected mailboxes before proceeding with detailed analysis.
Step 2: Review Individual Mailbox Statistics
Examine migration statistics for each mailbox included in the migration batch. Focus on mailboxes reporting warnings, synchronization delays, or failed status.
Verify:
- Number of migrated items
- Skipped items
- Failed items
- Synchronization duration
- Retry attempts
- Warning messages
- Completion status
Mailbox-level reports often reveal issues that are not immediately visible in the batch summary.
Step 3: Analyse Error Details
Review the first error recorded in the migration log, as it typically represents the underlying cause of subsequent failures. Determine whether the error relates to authentication, mailbox availability, permissions, connectivity, or mailbox data integrity.
When multiple errors are reported, classify them into:
- Configuration issues
- Environment-related issues
- Transient Exchange Online service conditions
- Mailbox-specific problems
This helps determine whether corrective action is required before rerunning the migration.
Step 4: Correlate Log Entries with Exchange Events
Compare migration timestamps with Exchange Online service health, maintenance activities, or network events that occurred during the migration window. For example, temporary service degradation or network interruptions may explain retry attempts, throttling events, or delayed mailbox synchronisation without indicating a permanent migration failure.
Step 5: Validate the Migration Endpoint
If multiple mailboxes fail with similar connectivity or authentication errors, verify the migration endpoint configuration.
Confirm:
- Endpoint connectivity
- Administrative credentials
- Exchange service accessibility
- Modern Authentication configuration
- Required network access
Endpoint validation helps eliminate configuration-related failures before additional migration attempts.
Step 6: Retry Failed Mailboxes
After correcting identified issues, rerun the migration for failed mailboxes rather than repeating the entire migration batch.
Review the updated migration logs to confirm that:
- Previous errors are no longer reported.
- Synchronization completes successfully.
- No additional warnings are generated.
- Mailbox statistics reflect successful processing.
Step 7: Perform Post-Migration Validation
Once all migration batches have completed successfully, validate the migrated mailboxes by comparing migration reports with the destination environment.
Confirm that:
- Mailboxes are accessible.
- Folder structure is intact.
- Mailbox item counts are within expected limits.
- Calendar, contacts, and mailbox folders are available.
- No unresolved warnings remain in the migration logs.
Post-migration validation ensures that successful log entries accurately reflect the migrated mailbox state.
Best Practices for Reviewing Migration Logs
Reviewing migration logs should be incorporated into every migration project rather than reserved for troubleshooting failed migrations.
Administrators should follow these recommendations:
- Review migration reports after every migration batch instead of waiting until the entire project is complete.
- Investigate mailboxes reporting Completed with Warnings before approving the migration.
- Monitor skipped and failed item counts to identify recurring data integrity issues.
- Use Exchange Online PowerShell reports for detailed diagnostics when graphical reports provide limited information.
- Perform incremental synchronisation before final mailbox cutover to capture recently modified mailbox data.
- Retain migration logs until user acceptance testing and post-migration verification have been completed.
- Document recurring migration issues and their resolutions to improve future migration planning.
- Compare migration reports with destination mailbox statistics to confirm successful synchronisation.
Implementing these practices helps identify issues early and reduces the likelihood of post-migration support incidents.
Conclusion
Migration logs are an essential diagnostic resource for Exchange Online mailbox migrations, providing detailed insight into mailbox processing, synchronisation progress, skipped items, warnings, and migration failures. While migration batch status offers a high-level overview, detailed migration reports and mailbox statistics enable administrators to identify the exact cause of migration issues and verify successful data transfer.
A structured approach to reviewing migration logs, including analysing mailbox statistics, interpreting error details, validating migration endpoints, and confirming post-migration results, helps reduce downtime and ensures a reliable migration process. Regular log analysis also supports performance optimization and simplifies troubleshooting for future migration projects.
When planning or validating Exchange Online mailbox migrations, administrators should regularly review migration logs to verify successful mailbox processing, identify failures, and confirm data integrity. This approach aligns with the migration guidance and technical documentation provided by EdbMails.
Frequently Asked Questions
What information is included in Exchange Online migration logs?
Where can I view migration logs in Exchange Online?
Why does a migration batch show Completed with Warnings?
What causes skipped mailbox items during migration?
How can I troubleshoot authentication errors reported in migration logs?
Should migration logs be retained after the migration is complete?
When should I perform an incremental migration?
