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Detached Attachments

Target mail platforms will reject messages from migrating if the message size (message body + attachments) exceeds the platform’s defined size limits. As a result, Transend Migration Console includes logic that detaches attachments that exceed the defined limits so that the message will continue to migrate. Detached attachments are either stored in a cloud-based user drive (i.e. OneDrive or Google Drive) or in a local directory on the migration machine (if migrating to a platform other than Microsoft 365 or Google Workspace).

Understanding source and target mailbox storage differences

Detached attachments are a common reason why the total storage consumed by a target mailbox may differ from the storage reported in the source mailbox after migration. When an individual attachment, or the combined size of a message body, embedded objects, and attachments exceeds the target platform’s supported size limits, one or more attachments are detached from the migrated message so that the underlying message can migrate successfully.

Because detached attachments are stored outside the target mailbox (i.e. in OneDrive, Google Drive or in a local directory on the migration machine), their file sizes are not included in the target mailbox’s reported storage consumption. As a result, even when the migration has completed successfully and the expected messages are present, the target mailbox may display a lower storage value than the source mailbox. The cumulative size of detached attachments can therefore account for some or all of the apparent storage discrepancy between the source and target environments.

Note: The cumulative storage associated with detached attachments is calculated and displayed in Transend Migration Console only after the mailbox migration has completed. Detached attachment storage totals are not updated dynamically while a migration is in progress. However, individual attachments that are detached are logged in the Detached Attachment window of the User Results page as they are encountered during migration, allowing administrators to review and identify specific detached attachments while the migration is still in progress. Once the mailbox migration is complete, the cumulative detached attachment storage value can be used to help reconcile differences between source and target mailbox storage.

Adjust the max message and attachment size allowed by target system

The Set maximum message and attachment size allowed by target system option allows you to customize the maximum message size to be migrated to the target system.