Turn off Cached Mode to fix Outlook syncing issues

Summary: Microsoft Outlook provides two different connectivity modes, Cached Exchange Mode and Online Mode, when you add or sign into the Outlook client on Windows or Mac. The Cached Exchange Mode, also referred to as Offline Mode or Work Offline, is the default connectivity mode for Office 365 accounts. However, users can switch between Cached Exchange Mode and Online Mode by turning off the Cached Exchange Mode via Outlook options to resolve Outlook issues. In this guide, we have discussed the cached Exchange Mode with reasons and steps to turn off work offline mode in Outlook.

Cached Exchange mode is an Outlook feature that enables Outlook users to access and use their accounts when the internet is unreliable, slow, or unavailable. The mail items, such as emails, contacts, attachments, notes, calendar items, etc., are cached and stored locally in an Outlook OST (Offline Storage Table) file.

The changes made offline are stored in the OST file and synced with the Exchange Server when the system goes online or connects to the Exchange Server. By default, 12 months of your mailbox data is stored in the local cache. However, you can change this setting and control how many mail items Outlook can keep offline.

Turn Cached Exchange Mode on or off

1. Click File>Account Settings>Account Settings.

   

2. Click the Exchange or Microsoft 365, and then click Change.

   

3. Under Offline Settings, check Use Cached Exchange Mode to download email to an Outlook data file.

4. Exit, and then restart Outlook.

If you want to turn on Cached Exchange Mode, repeat the steps, but checkmark Use Cached Exchange Mode.

By default, 12 months of your email is available offline, but you can control how much mail is kept offline.

Reasons to Turn Off Cached Exchange Mode

There could be various reasons to turn off the Cached Exchange Mode. For instance, when the local cache or OST file grows larger, it consumes the local storage space and may lead to performance issues in Outlook.

Cached Exchange Mode also works with Shared Folders in Microsoft Outlook 2010 and later versions. This allows Outlook users to add another user’s mailbox or shared folder to your profile. As a result, all items that you have access to are downloaded in the local cache (OST) that can significantly increase the OST file size.

However, an OST file becomes vulnerable to damage due to integrity issues caused by large size (oversizing).

Fun Fact: Local cache stored in .ost files is 50-80% larger than the mailbox size on the Exchange Server.

In addition, Outlook takes more time to fetch the information and may fail to locate emails in search. There could also be delays in mailbox synchronization, or sync errors may occur that can prevent users from sending or receiving new emails and lead to send/receive errors in Outlook or cause conflicts in shared folder.

An email message sent by an Outlook user is not sent immediately to the addressee. It may remain in the ‘Outbox’ of your Outlook account for up to one minute until the next synchronization starts. Users need to manually click the Send All button under the Send/Receive tab to send the email immediately.

However, you can resolve the sync errors and other common Outlook issues, such as send/receive errors, by turning off the Cached Exchange Mode in Outlook.

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