How to Plan and Configure Cached Exchange Mode in Outlook?

Summary: This article explains what’s Outlook Cached Exchange Mode and how it works. We have provided stepwise instructions to configure Cached Exchange Mode in different Outlook versions. We have also mentioned about a software that can help you access an orphaned OST file.

How to Plan and Configure Cached Exchange Mode in Outlook?

Cached Exchange Mode is an Exchange connectivity mode that offers a seamless online and offline experience to users of Microsoft 365 and Microsoft Exchange Server mailboxes. In this mode, Outlook caches your Exchange mailbox and Offline Address Book (OAB) on your local system. Technically, it creates a replica of your Exchange mailbox in an Offline Storage Table (.OST) file.

Also Read: How to Change the Location of Outlook OST?

When Outlook Cached Exchange Mode is enabled, you don’t have to depend on Internet connectivity to access your mailbox. It allows you to work offline and to perform different actions, such as read/write emails, search emails, etc. Outlook automatically updates the cached data, whenever you are online, by connecting with the Exchange mailbox.

Should I Use Cached Exchange Mode?

Cached Exchange Mode is recommended, if you:

  • Frequently move in and out of Internet connectivity.
  • Work offline for long periods.
  • Use an Internet connection that has a high-latency (500 ms or above) to the Exchange Server.

Note: The OST file, created locally in Outlook Cached Mode, is much larger than the actual Exchange mailbox online. Generally, the .OST file is 50-80% larger than the mailbox size reported in Exchange Server. So, make sure you have adequate free space on your system to store the file.

How to Configure Cached Exchange Mode in Outlook 2013 and Later Versions?

To configure Outlook Cached Exchange Mode in Outlook 2013, 2016, and 2019, follow these steps:

  • Launch Outlook. Open the File tab and go to Account Settings > Account Settings.
  • Select the Exchange email account and click Change.
  • In the Exchange Account Settings window, select Use Cached Exchange Mode checkbox.
  • Select the appropriate value in the Download email for the past slider. You can pick a value from 3 days to All (all emails since the account was created), depending on your requirements. However, keep in mind that the longer the duration, the larger will be the size of OST file.
Download email for the past
  • Click More Settings. In the new window that opens, open the Advanced tab.
More Settings
  • Under Cached Exchange Mode Settings, select Download shared folders and Download Public Folder Favorites checkboxes, if desired. Then click OK.

Note: Shared folders include Exchange Public Folders, SharePoint folders, etc.

  • Click Next and then click Done to finish the process. 

How to Configure Cached Exchange Mode in Outlook 2010?

To configure Cached Exchange Mode in Outlook 2010, follow these steps:

  • Open the File tab.
  • Go to Account Settings > Account Settings.
  • Under the Email tab, select the Exchange account and click Change.
  • Under the Microsoft Exchange server field, select the Use Cached Exchange Mode checkbox.
Use Cached Exchange Mode
  • Restart the Outlook.

For Outlook 2010 Cached Exchange Mode, you can change the download preferences as per your network connection.

To change download preferences in Outlook 2010, follow these steps:

  • Open the Send/Receive Tab.
  • In the Preferences section, click Download Preferences.
  • Select appropriate options.
Download Full Items

You can select the following download preferences in Outlook 2010 Cached Exchange Mode:

  • Download Full Items: Complete emails and attachments are downloaded.
  • Download Headers and Then Full Items: First, email headers are downloaded and then message bodies and attachments are downloaded.
  • Download Headers: Only email headers are downloaded. This reduces download duration and data amount.
  • On Slow Connections Download Only Headers: When using a slow network connection, message bodies and attachments aren’t downloaded. When a fast network connection is available, the download preferences are determined by your previous choices.

How to Configure Cached Exchange Mode in Outlook 2007?

To configure Cached Exchange Mode in Outlook 2007, follow these steps:

  • Open the Tools menu and select Account Settings.
  • Under the Email tab, select the Exchange account and click Change.
  • Under Microsoft Exchange server, select Use Cached Exchange Mode checkbox.
  • Restart Outlook 2007.

No Cached Exchange Mode in Your Outlook?

If you can’t find the Cached Exchange Mode in your Outlook, it could be because of the following reasons:

  • Non-Exchange Account: Outlook Cached Exchange Mode only works with Exchange Accounts (MAPI protocol). If you are using a POP3 or IMAP account, you can’t use this feature.
  • Disabled Feature: If your Exchange administrator has disabled the Cached Exchange Mode feature (for security reasons or otherwise), you can’t use it.
  • Microsoft Terminal Services: If Microsoft Terminal Services is installed on your computer, you can’t use Cached Exchange Mode.
  • Outlook Web Access: If you are accessing Outlook via Outlook Web Access (OWA), you can’t access Cached Exchange Mode.  

How to Access an Inaccessible OST File?

Outlook creates Offline Outlook Data File (OST) when you use Cached Exchange Mode. This file can only be accessed through the same Outlook application that creates it. If the OST becomes orphaned or inaccessible, you can delete the file and Outlook will recreate it automatically by synchronizing with your Exchange mail server.

Also Read: Recreate OST file in Microsoft Outlook 2007/ 2010/ 2013/ 2016/2019

If there is no Exchange connectivity, you can’t recreate the OST file. In such a case, you can use an advanced third-party tool, such as Stellar Converter for OST to convert OST file into PST format. This PST file can then be imported into any Outlook account.

Stellar Converter for OST is a trusted OST to PST converter tool that can safely convert inaccessible OST file into PST.

free download

Stellar Converter for OST Features

  • Converts all OST data to PST (emails, attachments, contacts, calendars, etc.)
  • Supports all Outlook versions
  • Saves OST items in multiple formats – PST, PDF, HTML, EML, MSG, and RTF
  • Offers preview of mailbox items before saving them
  • Allows you to save and load file scan information
  • Exports Outlook Contacts to CSV
  • Allows batch conversion – convert multiple OST files in a single batch (Technician edition)
  • Compacts and splits converted PST file (Technician edition)
  • Import OST into Office 365 and live Exchange (Technician edition)


Cached Exchange Mode is a notable Outlook feature that provides work stability even when there is poor or no Internet connectivity. By enabling this feature, you can work offline and perform a wide range of mailbox actions – read and write emails, download attachments, etc.

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