Outlook takes a long time to mark Calendar appointments as tentative - sniffer process is slow

Interesting this, at least i found it interesting as i had no idea this goes on. Mainly as im an Exchange person! Anyway, i still ended up looking into this...

The process in Outlook that inspects Calendar appointments and marks them as tentative (amongst other things it does) is the sniffer process.

Here is some nice info on it:

When you send out a meeting invite and the attendees respond to the meeting with Accept/Decline/Tentative responses, Outlook processes these responses either through the sniffer process, when you view the response in the Reading Pane, or when you open the response. When Outlook processes a response it locates the parent meeting (on the organizer's Calendar) for the response so the tracking tab on the meeting can be updated with the response type (Accept/Decline/Tentative) for the attendee.

POSSIBLE CAUSES:
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Following are common scenarios where Sniffer stops functioning or the owner loses the Sniffer Lock:
1. In Manager/Delegate scenario, Manager’s sniffer lock might be owned by delegate, if Manager’s outlook profile was closed and delegate is accessing manager’s calendar
2. 3rd party addin or application on the Outlook client causing Sniffer Process to stop functioning
3. If the user logs on to multiple Outlook client machines to access mailbox, the Sniffer lock will be moved to this Outlook client

We can carry out the following tests to check for the behaviour in different scenarios:

Scenario 1: Manager / Delegate:
1. Remove all the delegate from Users Outlook profile
2. Launch Outlook with the /sniff switch at least once. This is to make sure the Sniffer Lock remains with users Outlook profile
3. Make sure Outlook is launched normally, without the /sniff command switch
4. Try to reproduce the issue

Scenario 2: Third party addins or applications:
1. Check for 3rd party addin and applications on users client machine in the following registry path
a. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins
b. HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\Outlook\Addins
If we find any 3rd party addins in the above path, export the registry key(s) and check for the issue in Outlook
2. Also run Process Explorer to capture all the Dlls getting loaded with Outlook.exe
1. Start Outlook
2. Download and extract Process Explorer from
< https://www.microsoft.com/technet/sysinternals/ProcessesAndThreads/ProcessExplorer.mspx >
3. Double-click Procexp.exe
4. On the View menu make sure "Show lower pane" is checked.
5. Press CTRL + D
6. In the Process Explorer window, scroll down the list of files and then select Outlook.exe.
7. On the File menu click Save As
8. Save Outlook.exe.txt to your desktop and send it to me.
9. We will analyze the log file and check for any 3rd party Dlls.
10. If any 3rd party Dlls are present, we will disable/uninstall the associated application and check for the issue

Scenario 3: User logging on to multiple Outlook client machines
1. Check if user logs on to other Outlook client machines
2. If yes, the Sniffer lock will be moved to this Outlook client
3. If she doesn’t access her mailbox from multiple Outlook client, please ignore this scenario