Transporter Memory Issue During Microsoft 365 Backup

Product version: 11.0

Last modified: 24 July 2025

Problem

Microsoft 365 mailbox backup fails with the following error:

Error 267 – Backup of the "<mailbox name>" mailbox has failed – Transporter memory allocation error

This error typically causes the job status to be marked as failed for the affected mailbox, while other mailboxes in the same job may continue or complete successfully.

Background

This error indicates that the Transporter does not have enough allocated memory to perform the operation required to back up the specified Microsoft 365 mailbox.

This issue may occur with large or complex mailboxes or when multiple backup jobs are running concurrently.

Solution

To resolve this issue, do the following:

  1. Ensure that the Transporter has sufficient available RAM to handle the workload. Increase the physical memory on the Transporter VM.

  2. Go to Settings > Expert and increase heap size (system.transporter.modern.max.heap.size.megabyte) in the Expert Mode based on your system capacity (add 2 or 4 GB from the current value).

  3. If the problem persists after increasing memory and adjusting the heap size, create a Support Bundle, including relevant job logs and system configuration.