Use Sort to find large emails too, especially the "Size" and "Attachments" sort options. You can see the size of any subfolder and use that to determine where to focus the most time and effort.
Some places you might want to look for mail you can purge:
Don't forget to empty your Deleted Items Folder when you're done. Select the mail or mail folders you want to remove, and then right-click and choose Delete. It's also a great way to increase our mailbox size if we're not vigilant about deleting them when we're done! Unsubscribing from mailing lists that you no longer need means less email coming in, and a smaller mailbox. It's a great way to get reminders or alerts about things we're interested in. We all get email sent to us every day from websites or mailing lists we've signed up for.
Click OK to the Delete Folder confirmation dialog box.For each of the RSS Feeds (Microsoft at Home, Microsoft at Work, MSNBC News, Popular Government Questions from USA.gov and USA.gov Updates: News and Features), right-click the folder and choose Delete.Since they can be quite large, it's easier to do this through the Microsoft 365 Outlook WebApp, rather than through Outlook on your desktop, since the Web App doesn't have to synchronize the changes. Today, though, they just take up a lot of mailbox space, so if you have them, you should delete them. RSS feeds were part of the original upgrade to Outlook from GroupWise, and at one time were useful. It's a good idea to get rid of your RSS feeds. With the Info section selected you will find the size under Mailbox Settings.You'll need to use a combination of Outlook Web App and the Outlook Client. What solutions you might take will depend upon how close to the limit you are.