> Outlook Cached Mode is Greyed Out
> The Folder has not been updated when Outlook Cached Mode is enabled through GPO.
> Online Mode has no issues. 

Caution! Using Registry Editor incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

On ICA sessions , cache mode is greyed out on outlook
Created below registry on VDA machine and able to fix cache mode issue.
1. Open Registry Editor -:
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\OST]
DWORD : NoOST
Value = 3
Incase customer have MCS machines, update same registry on Master image and update catalog.




 

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Problem Cause

> Outlook Cached Mode is unchecked and greyed out
 

It is a Microsoft Outlook based configuration, where, we change the value to -: 0 = An OST is created by default and used for calendar caching. You can enable offline access and use the offline store. This is the default if the NoOST entry is missing. 1 = An OST is set up by default and used for calendar caching. Users cannot enable offline access or use the offline store. The options in the Exchange Server properties are not available. 2 = An OST is not set up by default and you cannot enable offline access or use an offline store. The options in the Microsoft Exchange Server properties are not available. 3 = An OST is not set up for Online mode. Users can enable offline access and use the offline store.

https://docs.citrix.com/en-us/profile-management/current-release/configure/enable-native-outlook-search-experience.html

https://docs.citrix.com/en-us/profile-management/current-release/integrate/outlook.html