Transaction logs not truncated at the end of an Exchange backup of types 'full' or 'Transaction Logs Only'.
VSS-based backups for non-Continuous Replication environments will truncate the transaction logs at the completion of Full or Transaction Logs-Only Backups.
After the backup is completed, the transaction logs are truncated by the Exchange Server, not by NetVault Backup.
In LCR and CCR environments, log truncation is delayed by the Microsoft Exchange Replication Service until all necessary log files are replayed into the replica copy.
Copy and Differential backups do not truncate the transaction log files.
Check the NetVault log for error messages. If a failed log truncation was reported back to NetVault, see solution 78860.
Ensure that circular logging is not enabled as this can cause logs to be reused and is not supported by NetVault.
In LCR and CCR environments, check that replication of the logs is performing as expected. Report any issues to Microsoft.
Progress the issue of 'Exchange failing to truncate logs after a successful backup' with Microsoft.