Hi @Salman Al Bedaiwi ,
The autocomplete cache in OWA is stored in the item of message class IPM.Configuration.Autocomplete and a hidden folder named Recipient Cache also contains cached recipient information that could be used for OWA users.
Based on my research and test, in order to empty these cache, a user would need to have an Outlook for Windows profile (Exchange Online mode) created and then delete the two objects using the MFCMAPI tool:
- Download and extract the MFCMAPI tool, launch MFCMAPI.exe, click OK, on the Session Menu, click Logon, select the Outlook profile for the mailbox, click OK.
- Double click the email address, right-click Root Container , and then click Open Associated Contents Table, arrange the columns header and scroll to the right until you can see the Message Class details for each entry, locate the object that has a Message Class ID of IPM.Configuration.Owa.AutocompleteCache to remove the OWA autocomplete.
- Expand Root Container - Top of Information Store - Contacts - Recipient Cache, right click on it, choose Delete folder, click Hard delete, OK:
I fully understand that you need to delete the cache for all users, but to the best of my knowledge, I'm afraid it's not feasible to be realized using the built-in Exchange feature or regular powershell. Given this, I'd recommend having a go using the steps above on one of the users, if it works, you can then share the procedure with all users so that they can remove the cache by themselves.
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