When you configure or add an Outlook.com, Exchange Server, or Office 365 account, Microsoft Outlook creates a synchronized copy of server mailbox items in an OST file (Offline Outlook Data File) on your local machine. Whenever you open MS Outlook, it immediately tries to connect to the mailbox server and synchronizes the mailbox items to and from the mailbox server. By default, synchronization is automatic. However, it may take a while to complete depending on the number of mail items to synchronize and network speed. For example, if you often receive multiple emails every day with large or several attachments, it may take much longer to synchronize the mailbox items and affect the Outlook performance. On the other hand, it will also consume a lot of mailbox storage on the server, which isn’t good unless server storage is not an issue. Furthermore, the synchronization may stop if the mailbox storage on the server exceeds the limit, preventing Outlook from sending or receiving new emails. Thus, sometimes, it becomes necessary to stop the synchronization of specific mail folders, especially those that receive or contain several emails with large attachments, to save mailbox storage and ensure uninterrupted email flow. In this article, we mention a few ways to stop synchronizing folders in Outlook 2016/2019. Ways to Stop Synchronizing Folders in Outlook Based on your preference, you may choose to either completely or partially stop synchronizing folders in Outlook 2016 or Outlook 2019. Below we have mentioned some simple methods to pause or stop emails or folder synchronization in Outlook. Method 1: Completely Stop Folder Synchronization When you use an IMAP email account in Outlook, such as Gmail or Hotmail, Outlook provides you with options to subscribe or unsubscribe folders. When an email folder is subscribed, it’s automatically synchronized. Similarly, if you want to stop synchronizing an email folder, you can unsubscribe from the folder. Follow these steps: Right-click on the folder for which you want to stop synchronization and choose IMAP Folders… Click the subscribe tab and then click Query. Select all the Subscribed folders you want to unsubscribe and click the Unsubscribe When prompted, click OK. This will stop synchronizing selected/unsubscribed folders in your Outlook IMAP account. Method 2: Use Work Offline Option In Outlook, you can switch between Online and Offline mode. In Offline mode, mail items and folders are synchronized between the Outlook data file and mailbox server. In Online Mode, Outlook does not synchronize emails or mail folders. Instead, Outlook connects directly to the mailbox server. You can enable Online Mode by disabling the Cached Exchange Mode permanently, discussed in the next method. However, if you want to stop synchronizing mailbox folders temporarily, go to Send/Receive and click Work Offline. This will disconnect you from the server and stop synchronizing the folders. In addition, you won’t be able to send or receive new emails. Method 3: Disable Cached Exchange Mode If you use Outlook to access Office 365 or Exchange Server-based email account, you can disable Cached Exchange Mode to stop synchronizing the folders. Note: You can’t disable Cached Exchange Mode when using an Outlook.com account. To disable Cached Exchange Mode and stop folder synchronization in Outlook 2016 or 2019, follow these steps: In Outlook 2016 or 2019, navigate to File > Account Settings > Account Settings. Select your Office 365or Exchange email account from the list and click Change. Uncheck the Cached Exchange Mode option under Offline Settings click next and then click OK when the prompt appears. Click Finish and then restart Outlook for changes to take effect. Method 4: Disable Folder Synchronization Option You may also disable the automatic synchronization feature to stop synchronizing folders in Outlook 2016 or 2019. The steps are as follows: In Microsoft Outlook 2016 or Outlook 2019, go to File > Options. Click Advanced and then scroll down to the Send and receive Uncheck the Send Immediately When Connected Then click the Send/Receive button and deselect “Perform automatic send/receive when exiting”. Click, OK, to apply the changes and update the settings. From now onwards, automatic synchronization of email folders in your Outlook 2016 or 2019 will stop. Conclusion Sometimes, you may require to stop synchronizing email folders in Outlook to save the mail items locally and conserve the mailbox server storage. Besides, slow synchronization can adversely impact Outlook performance on old systems or systems with a poor network connection. In this article, we have shared some simple methods to stop synchronizing the folders in Outlook 2016 and Outlook 2019. However, if you want to stop folder synchronization due to errors you are receiving while sending or receiving new emails, it could be due to a damaged Outlook data file (OST). You can convert such inaccessible OST files into Outlook importable PST files by using an OST to PST converter tool, such as Stellar Converter for OST. The software can help restore the lost mail items to a new PST file, existing Outlook account, Office 365, or Exchange Server.