How to Track Outlook Sync Status Per Folder With MFCMapi

When Outlook fails to sync specific folders, you may see stale data or missing emails in one folder while others update normally. The cause is often a corrupted synchronization state or a folder-level sync failure that Outlook does not clearly report. This article shows how to use MFCMapi, a free Microsoft tool, to inspect the sync status of each folder and identify which folders are not synchronized correctly.

What MFCMapi Reveals About Folder Sync Status

MFCMapi (Microsoft Exchange Server MAPI Editor) is a developer tool that reads MAPI properties hidden from Outlook. When Outlook syncs folders in Cached Exchange Mode or an Online Archive, it stores sync flags and counters as MAPI properties on each folder. These properties tell you whether the folder is configured to sync, when the last sync occurred, and how many items the server reports.

The tool does not modify Outlook data unless you manually change a property. You use it only to read diagnostic values. Before you start, close Outlook. MFCMapi needs exclusive access to the profile to read live data without conflicts.

No prerequisites are needed beyond downloading MFCMapi from the Microsoft website. Windows 11 and Windows 10 both support the tool. You do not need Exchange admin rights because MFCMapi works against the local Outlook profile cache.

Steps to Check Sync Status of Any Outlook Folder

1. Download and launch MFCMapi
   Go to the official Microsoft download page for MFCMapi and save the executable. Run the file as administrator. If you see a security warning, click Run.
2. Log on to your Outlook profile
   In MFCMapi, click Session in the top menu, then click Logon. Select the Outlook profile that contains the mailbox you want to inspect. Click OK. A tree view appears showing MAPI stores including your mailbox and any archive.
3. Open the mailbox store
   Double-click the entry named Mailbox – Your Name or the default Exchange store. The tree expands to show Root Container, Top of Information Store, and all folder hierarchies.
4. Navigate to the folder you want to check
   Expand Top of Information Store. Right-click the folder name such as Inbox or Sent Items. From the context menu, choose Display Properties.
5. Find the sync-related properties
   In the Properties window, look for these tags:
   – PR_SYNCHRONIZE_FLAGS (tag 0x66350003): Value 1 means sync is enabled. Value 0 means the folder is excluded from sync.
   – PR_CONTAINER_CONTENTS_UNREAD (tag 0x36020003): Shows the unread count on the server. Compare this to the unread count shown in Outlook to see if the folder is behind.
   – PR_LOCAL_COMMIT_TIME_MAX (tag 0x0E0F0040): The last time the folder was modified locally. A very old date indicates the folder stopped syncing.
6. Check the sync state for public folders or archives
   For public folders, expand Public Folders in the tree instead of Top of Information Store. For an Online Archive, expand the archive store entry. Repeat steps 4 and 5 for each folder.
7. Interpret the values
   If PR_SYNCHRONIZE_FLAGS is 0 for a folder you expect to sync, Outlook has excluded it. If PR_CONTAINER_CONTENTS_UNREAD shows a number that never changes, the folder may have a sync failure. Note the values and close the Properties window.

Common Sync Failures You Can Detect With MFCMapi

Folder shows PR_SYNCHRONIZE_FLAGS = 0 even though sync is enabled in Outlook

This means the folder is not included in the Cached Exchange Mode sync list. The cause is often a corrupt sync filter or a previous manual exclusion. To fix this, open Outlook, go to File > Account Settings > Account Settings, double-click your Exchange account, and click More Settings. Under Advanced, click Send/Receive. Make sure the folder is checked. Then close Outlook and reopen MFCMapi to verify the flag changed to 1.

PR_CONTAINER_CONTENTS_UNREAD stays at zero or a stale number

If the unread count on the server never changes despite new emails arriving, the folder is not receiving updates from the server. This usually points to a corrupt local cache. The fix is to disable Cached Exchange Mode for that profile, restart Outlook, then re-enable Cached Exchange Mode. This rebuilds the local copy of the folder.

PR_LOCAL_COMMIT_TIME_MAX shows a date older than today

A local commit time that is days or weeks old means Outlook has stopped writing changes to that folder. This can happen when the .ost file reaches its size limit or when the folder contains a corrupted item. Run the Outlook Inbox Repair Tool (scanpst.exe) on the .ost file, then restart Outlook and check the property again.

MFCMapi Property Names vs Outlook Behavior: Key Differences

Item	MFCMapi Property	Outlook Behavior
Sync enabled flag	PR_SYNCHRONIZE_FLAGS (0x66350003)	Outlook does not display this flag in any settings dialog
Server unread count	PR_CONTAINER_CONTENTS_UNREAD (0x36020003)	Outlook shows local unread count, not server count
Last local modification time	PR_LOCAL_COMMIT_TIME_MAX (0x0E0F0040)	Outlook does not expose this timestamp in the UI
Folder hierarchy sync status	PR_FOLDER_CHILD_COUNT (0x360A0003)	Outlook shows folder count after sync completes

MFCMapi properties provide server-side or cache-side values that Outlook hides. When you see a mismatch between what Outlook shows and what MFCMapi reports, the folder sync is likely broken. Use the property values to decide whether to rebuild the cache, run scanpst.exe, or adjust Send/Receive settings.

You can now inspect any folder in your Outlook profile and determine if it is syncing correctly. Next time you suspect a folder is not updating, open MFCMapi and check PR_SYNCHRONIZE_FLAGS and PR_CONTAINER_CONTENTS_UNREAD before trying more aggressive fixes. For advanced troubleshooting, write down the property values before and after running scanpst.exe to confirm the repair restored sync.