If you find yourself staring at the long-spinning beach ball, then your email client is most likely experiencing some severe performance issues. There can be multiple reasons for why Outlook isn’t very efficient. But here are some things you can check and do at your end to improve the performance:
Folder count: Keep a maximum folder count of 500 for each identity. This count includes local folders or On My Computer folders. In fact, it is a good practice to maintain less than 100 folders each in calendar, contacts, tasks, and notes.
Item s count: Keep a maximum of 20,000 items each in the Inbox and Sent Items folders (includes the folders and subfolders). For optimal performance, keeping less than 5000 items each in calendar, contacts, tasks, and notes folders is highly recommended.
Mailbox size: Your mailbox limit might be much greater, but it’s best to keep your mailbox size under 9 GB to ensure better performance and prevent any potential stability issues.
If you still see performance issues despite following the above recommendations, send your questions to the Microsoft Community.