Corrective update on the mailbox server

We applied a corrective update to the mailbox server so that the fault behind the related incident cannot recur.

The update changes how the overnight maintenance task handles large mailboxes, which is what led to the outage earlier this morning. Mailbox access was interrupted for about five minutes while the update was installed; incoming mail was held during that time and delivered immediately afterwards. We then ran the previously affected task again and confirmed that it now completes as intended.