1. Check if there are emails stored in the Deleted folder.
2. Ensure that no email messages have been forwarded multiple times as the email size is cumulative when forwarded.
3. Empty the Trash folder if there are emails in it.
4. Unarchive messages that are located in the Archive folder.
5. Check for large attachments such as image files and videos and delete these to free up storage space.
6. Keep an eye on the mailbox size by clicking on Configure, selecting Mailbox Settings and Display mailbox size for a quarterly review.