An administrator had a question about having Outlook in online mode, yet an OST file was created.
I have Outlook Cached Mode disabled in Group Policy so that no one can turn it on and yet OST files get created. When I open Outlook, the status bar says it's online, but after about 2 seconds you will get the Send & Receive status bar for the account and the OST file in the %localappdata%\microsoft\outlook folder grows.
Outlook has one Online mode but two offline modes: Exchange Cached mode and Offline Folders. Although Outlook 2013 doesn't use true offline folders, only cached mode, you need to disable offline folders along with cached mode to prevent it and older versions of Outlook from creating an OST file for offline use.
You can disable offline use using group policy or by setting a registry value.
In the Group Policy editor, go to Microsoft Outlook/Account Settings/Exchange and set Do not allow an OST file to be created to Enable. In the Cached Exchange mode folder, set Use Cached Exchange mode for new and existing Outlook profiles to disabled.
These policies will set the following registry values
HKEY_CURRENT_USER\Software\Policies\Microsoft\office\15.0\outlook\cached mode
DWORD: enable
Value: 0
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\OST
DWORD: NoOST
Value: 2
NoOst value specifies whether or not an OST is created at startup. Setting the NoOst value to 2 will prevent the use of OST files. A value of 3 will allow OST files for cached mode but won't create one when online mode is used.
| Value | Description |
|---|---|
| 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. |
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12 Comments on "Outlook Online mode creates an OST file"
what if i want to only have the Address Book online but keep the emails in OST? how to do it for Outlook 2016?
i found this registry key is it correct for my purpose?
HKEY_CURRENT_USER\Software\Microsoft\Office\nn.0\Outlook\Cached Mode Parameter: DownloadOAB Type: REG_DWORD Value: 0
The address book (OAB) and ost are separate. The OAB is basically a copy of your organizations Active Directory. Outlook will typically download a copy of the OAB so you have it when offline but you also have access to the online address book in the Address book dialog.
The OAB is separate from the contacts in your mailbox. If you only want mail, not calendar & contacts, you can set the account up as IMAP.
Hi, i was having pop email configured in outlook, now i have upgraded my email and now i want to switch to IMAP. After configuring outlook mail in IMAP its creating OST file which stores in C drive. How can i change the location of OST file from C to D Drive like i was doing in POP mail with PST file.
Sorry I missed this earlier. You need to set a reg key before you create the profile or you can try using junction points. See https://www.slipstick.com/outlook/config/how-to-move-the-imap-personal-folder-pst/ for more information. This will work with all imap account, whether they create an ost or pst.
Hi, this is an old post, but i try..
When I disable cached mode and the creation of OST file, the outlook client connects online and my userprofile free of OST file.
BUT, snipping tool and Adobe reader cannot use their "send to email" functionality. I have tried different settings on and off with cached mode vs disallow ost file creation, but it seems that to make it work both cached mode and OST file must be on... Strange.. I want to keep my profile as slim as possible. Seen this before?
Thanks Diane! And I"m guessing that you still had your IMAP OST, because Outlook treats it like a PST - which aligns with the fact that you can re-route it using ForcePST, even though it's an OST file. :)
Exactly. But I still didn't trust Microsoft not to screw things up. LOL
Hello Diane - does this "no OST" setting also prevent the OST creation that happens when you add an IMAP account to Outlook 2013? I know that they have changed IMAP functionality, and I'm not sure if these 2 are connected or not.
Thanks!
Karl
No, it should not (but I'll double check) - the IMAP ost are treated as pst files.
I was able to create an imap account in Outlook 2016 while using the noost key (set to disallow ost). When i restarted outlook with an exchange account, it went into online mode.
Hi Mam.
I need to know about the ost file offline configuration, I have ost file backup of my colleague which have left the company, and now i need to connected that ost find file in Oultook 2013,
So how can i connected in offline mode in that ost file to view the mail conversion.
Thanks for advance...
You cannot open his ost file on your computer. If the mailbox was deleted and his computer/outlook profile no longer available (if you can open his outlook offline, you can export to a pst file), you'll need to use a 3rd party recovery utility to access the mail. See the tools section for utilities - https://www.slipstick.com/problems/pst-repair/convert-an-exchange-offline-file-ost-to-a-personal-file-pst/#tools