This process will help you improve the performance of Microsoft Outlook with IMAP/Gmail:
1. Press Ctrl+Alt+S to open your Outlook Send and Receive groups.Select the IMAP/Gmail account that you have configured with Microsoft Outlook and click Edit.
2. *If the shortcut Alt + Ctrl + S doesn’t work in your version of Outlook, go to Tools -> Send/Receive, Send/Receive Settings, and then click Define Send/Receive Groups.
3. The next screen will have all the default IMAP/Gmail folders (like All Mail, Trash, Inbox, Spam, etc) – For Spam and Trash folders, select “Download headers only”. For Inbox and Drafts, select “Download complete item including attachments.” Press OK.
*This prevents Outlook from downloading mails and attachments that are marked as Spam by Gmail*
4. when you press OK, it takes back to the previous Send and Receive groups screen.
5. Here adjust the time that Outlook should wait before checking for new email on IMAP/Gmail server.
Note: If you want Microsoft Outlook to load the default IMAP/Gmai Inbox folder during start-up, go to Tools -> Options (Other) -> Advanced Options and browse for your IMAP/Gmai Inbox folder.