4. Run Mailbox Tools

Newer versions of Outlook also have some great built-in tools to clean up and reduce the size of your main PST file. Just click on File and then click on Tools.
You’ll see three options here: Mailbox Cleanup, Empty Deleted Items Folder and Clean Up Old Items. Mailbox cleanup has several tools that you can use to archive emails, empty the deleted items folder and an option to help you find the largest emails in your Outlook data file.
The AutoArchive function is the most important as it will move all the older emails to a separate PST file, which will make things run a lot smoother. If you have thousands of emails in many different folders, Outlook will run slow on most systems.

5. Use Cached Exchange Mode

If you have an account that is connected to Microsoft Exchange, then you should make sure Cached Exchange Mode is enabled. You can do this by clicking on File, then Account Settings and then clicking on the Change button for the account listed on the Email tab.
This will keep the most recent mail offline, so everything will load faster when you access those recent emails. You can also download more emails if you like by adjusting time frame.

That’s all of the methods I could figure out so far! If you know of any other method that will help speed up the super slow Outlook, do post a comment and let us know! Also, if you’re having trouble starting Outlook, check out my other post. Enjoy!