What is Cached Exchange mode in Outlook?

What is Cached Exchange mode?

Cached Exchange mode is a feature in Microsoft Outlook that stores a copy of a user's Exchange mailbox on their computer. This mode enables the user to access their mailbox data locally from the offline data file (.ost) even when an Internet connection is not available.

In this mode, when users open a mailbox item, such as an email, contact, or calendar item, Outlook first checks the cache to see if the latest version of the mailbox item is available. If the latest version is available, Outlook displays it. If not, Outlook queries the Exchange server for the latest version of the item.

Cached Exchange mode also speeds up the opening of Outlook items and reduces server load, as it eliminates the need to repeatedly query the Exchange server for the same information. For instance, if Outlook 365 is not updating inbox automatically, the Cached Exchange mode helps to retrieve emails from the local OST file.

Overall, Cached Exchange mode provides users with offline access to their Exchange mailbox, while also improving the performance and efficiency of the Outlook application.

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Outlook 365 Cached Exchange mode

Benefits of using the Cached exchange mode in Outlook

Cached Exchange Mode was introduced in Microsoft Outlook 2003 and is available in all the recent versions of Outlook such as 2021, 2019, 2016, 2013, 2010 and 2007. There are several benefits of using Cached Exchange mode in Outlook, which are listed in the following points.

Offline Access to your mailboxes: One of the main benefits of Cached Exchange mode is that it enables you to access your mailbox data even when an Internet connection is not available. This is because a copy of the Exchange mailbox is stored on your computer in the form of an OST file, providing offline access to email, contacts, and calendar items.
Improved Outlook Performance: Cached Exchange mode can greatly improve the performance of Outlook by reducing the number of server requests. When you open a mailbox item such as an email, contact or a calendar entry, Outlook checks the cache first to see if the latest version is available, eliminating the need to repeatedly query the Exchange server for the same information.
Reduced Email Server Load: Cached Exchange mode lowers the load on the Exchange server by reducing the number of requests to the server. This factor can help to improve the Exchange environment's overall performance and stability.
Better Outlook Responsiveness: Cached Exchange mode can also result in faster item access and better responsiveness in Outlook, because the cached data is stored locally on your computer and is therefore quickly accessible.
Improved Data Synchronization: Cached Exchange mode can also help sync Outlook email, as changes made to items in the cache are automatically synchronized with the Exchange server the next time the user connects to the server.

Limitations of Outlook Cached Exchange mode

While Cached Exchange mode provides several benefits to Outlook users, there are also some limitations to be aware of:

Increased Disk Space on the computer: Storing a copy of the Exchange mailbox on your computer requires a significant amount of disk space, which can be a concern if you have limited storage on your computer.
Delayed data updates and slower performance: Cached Exchange mode can result in delayed updates to mailbox data, as changes made on the Exchange server may not be reflected in the cache until you connect to the server and the cache is synchronized. It can also make Outlook run more slowly, particularly when synchronizing a large mailbox for the first time.
Data Loss and Corruption issues: Cached Exchange mode creates an OST file that may become inaccessible if your Exchange server goes down. When the OST grows in size, it can become corrupted, potentially resulting in data loss and causing Outlook synchronization issues.
Limited Functionality: Cached Exchange mode may also have limited functionality compared to working directly with the Exchange server, as certain features, such as public folder access, may not be available in cached mode.

Differences between Cached mode and Online mode

Cached Exchange mode is a mode in which a copy of your Exchange mailbox is stored on the local computer, enabling offline access to email, contacts, and calendar items. In this mode, changes made to items in the cache are automatically synchronized with the Exchange server the next time you connect to the email server.

The Online mode, on the other hand, is a mode in which all data is stored on the Exchange server and accessed by connecting directly to the server in real-time. You do not have offline access to your mailbox in this mode and must have an active Internet connection to access the mailbox data. The following table illustrates the difference between the two modes.

Feature	Cached Exchange Mode	Online Mode
Offline Access	Yes	No
Performance	Improved	Slower
Server Load	Reduced	Increased
Responsiveness	Faster	Slower
Data Synchronization	Improved	Delayed
Disk Space	Increased	No Impact
Functionality	Limited	Full

How to know if Outlook is running in cached mode?

To determine whether Microsoft Outlook is running in Cached Exchange mode or Online mode, follow these steps:

Step 1: Open Outlook and go to Account Settings
- Start Outlook, go to ‘File’ > ‘Account Settings’ > ‘Account Settings’
- In the Account Settings window, select the email account you want to check and click ‘Change’.
Step 2: Access More Settings for your email account
- In the Change Account window, click ‘More Settings’.
- In the Microsoft Exchange dialog box, go to the ‘Advanced’ tab.
Step 3: Check the Cached Exchange mode setting
- In the ‘Advanced’ tab, look for the option ‘Use Cached Exchange Mode’
- If the checkbox is selected, Outlook is running in Cached Exchange mode.
- If the checkbox is unselected, Outlook is running in Online mode.

What does disabling the cache mode in Outlook do?

Disabling the Cached Exchange mode in Microsoft Outlook means that the application no longer stores a copy of your Exchange mailbox on the local computer. Instead, you will have to access the mailbox directly on the Exchange server in real-time, without any local cache.

Disabling the cache mode frees up the disk space used to store the local copy of the Exchange mailbox, and changes made to items in the mailbox will be reflected in real-time. However, disabling the cache mode may result in slower performance and responsiveness in Outlook, as the application will no longer have a local copy of the mailbox data to work with. Additionally, if you have poor Internet connectivity, you may experience issues accessing your mailbox data.

How to turn off Cached Exchange mode in Outlook 365?

To turn off Cached Exchange mode in Outlook 2016, 2019 and 2013 follow these steps:

Note: that these steps may vary slightly in different versions of Outlook, but the general process for turning off Cached Exchange mode should be similar in most cases.

Step 1: Open Account Settings and select the email account
- Open Outlook and go to ‘File’ > ‘Account Settings’ > ‘Account Settings’.
- In the Account Settings window, select the email account for which you want to turn off Cached Exchange mode and click ‘Change’.
Step 2: Access More Settings in Outlook and click Advanced
- In the Change Account window, click the ‘More Settings’ button.
- Open Microsoft Exchange Dialog Box: In the Microsoft Exchange dialog box, go to the ‘Advanced’ tab.
Step 3: Disable the Cached Exchange Mode Setting
- In the ‘Advanced’ tab, uncheck the ‘Use Cached Exchange Mode’ checkbox.
- Click ‘OK’ to save the changes and close the dialog boxes.
- Close Microsoft Outlook and then restart the application for the changes to take effect.

How to turn on Cached Exchange mode in Outlook?

To enable the cached Exchange mode in Exchange 2010, 2013, 2016 and 2019 follow these steps:

Step 1: Open Account Settings in Outlook
- Go to ‘File’ > ‘Account Settings’ > ‘Account Settings’.
Step 2: Select the email account and access more settings
- In the Account Settings window, select the email account for which you want to turn on Cached Exchange mode and click ‘Change’
- In the Change Account window, click the ‘More Settings’ button.
- In the Microsoft Exchange dialog box, go to the ‘Advanced’ tab.
Step 3: Enable the Cached Exchange Mode Setting
- In the ‘Advanced’ tab, check the ‘Use Cached Exchange Mode’ checkbox.
- Click ‘OK’ to save the changes and close the dialog boxes.
- Close Microsoft Outlook and then restart the application for the changes to take effect.

Shared folders cached mode

Shared folders in Microsoft Outlook refer to folders that are shared by multiple users within an organization. These folders may include calendars, contacts, tasks, and other items, and they can be accessed and modified by authorized users. Outlook downloads these folders to the local cache when you enable the cached mode for shared folders. Follow the steps to enable cached mode for the shared folders and Public folder favorites.

Step 1: Open Outlook and go to Account Settings:
- Start Outlook on your computer
- Go to ‘File’ > ‘Account Settings’> ‘Account Settings’
Step 2: Select the Email Account and go to more settings
- In the Account Settings window, select the email account for which you want to turn on Cached Exchange mode for shared folders and click ‘Change’.
- In the Change Account window, click the ‘More Settings’ button.
- In the Microsoft Exchange dialog box, go to the ‘Advanced’ tab.
Step 3: Enable the Cached Exchange mode for Shared folders
- In the ‘Advanced’ tab, select the ‘Use Cached Exchange Mode’ option.
- In the Send/Receive Settings window, change the sync frequency to a lower value, such as 5 or 10 minutes.
- Select the option ‘Download Shared Folders’, which enables Cached Exchange mode for the shared folders that are associated with the email account.
- You can also enable ‘Download Public folder Favorites’, if you want to keep a copy of them.
- Click ‘OK’ to save the changes and close the dialog boxes.
- Close Microsoft Outlook and then restart it for the changes to take effect.

Why is the Microsoft Outlook Cached Exchange mode unavailable?

The Microsoft Outlook Cached Exchange mode may be unavailable in certain scenarios, such as:

Email Account Configuration: Cached Exchange mode may not be available if the email account is not configured as an Exchange account in Outlook.
Older Version of Outlook: Cached Exchange mode may not be available in older versions of Outlook such as 2000 that do not support this feature.
Restricted User Permissions: If the user does not have sufficient permissions to access the shared folders associated with the Exchange account, Cached Exchange mode may be unavailable. The feature may also be disabled by the Exchange administrator.
Installation of Microsoft Terminal: If you are running a Windows Server with Microsoft Terminal installed, Cached mode will be unavailable.

How to recover emails from an inaccessible OST file?

An OST (Offline Storage Table) file is a local copy of a user's Exchange mailbox that is created when you enable the Cached Exchange Mode in Outlook. Several reasons such as Exchange server crashes, abrupt system shutdowns, virus and malware infection and Outlook crash can cause the OST file to become inaccessible or orphaned. In such cases, Outlook fails to synchronize with the Exchange server and fetch new emails.

EdbMails OST to PST Converter is a reliable software that can help recover emails from inaccessible or orphaned OST files. The software provides a simple approach for converting OST to PST which can then be imported into Outlook.