Outlook sync issues cause emails to be stuck in the Outbox and undeliverable mail items

Last Updated: June 20, 2024

ISSUE

When you send emails, you may find they get stuck in the Outbox. If you check the Sync Issues folder, you may find errors similar to below. 

SyncMonitor triggered for Inbox (80040611) 
Error synchronizing folder [80040611-3EE-80040611-560] 
Unknown Error: 
Microsoft Exchange Information Store

80040611 means MAPI_E_NOT_ENOUGH_NAMED_IDS.

When you send meeting items, you may see a Non-Delivery Report or Undeliverable message with the following specifics: 

Remote server returned '554 5.2.0 STOREDRV.Deliver.Exception:StoragePermanentException; Failed to process message due to a permanent exception with message [BeginDiagnosticData]Invalid named property: ***. StoragePermanentException: Invalid named property: ***

This issue can occur when the mailbox contains a very large number of properties in the PublicString namespace, which is exhausting the quota for that namespace. When the property quota is exceeded the Outlook OST and mailbox are broken and cannot be used further.

STATUS: WORKAROUND

Recent cases with this issue have found that Digital Guardian is creating the excess properties. This issue has been escalated to Digital Guardian for a fix. 

To work around the issue, pause usage of Digital Guardian until they provide a fix. To mitigate, the issue requires a mailbox move and then recreating the Outlook OST. To request a mailbox move, open a support case from the Microsoft 365 Admin Portal and reference this article.

Additional Resources

Outlook extended properties overview