I have DreamHost shared unlimited hosting. I got e-mail that one of my “users and/or mailboxes of yours are within 10% of their disk space limit,” 220 MB out of 200. But according to Thunderbird IMAP client, she only had ~130 MB in her IMAP Inbox, and the warning didn’t go away after deleting more e-mail.
Tip for Thunderbird: I noticed that Thunderbird didn’t show a Trash subfolder of her IMAP Inbox. I’m not sure why, other e-mail accounts do. To make it show I went to Account Settings > Server Settings > Advanced, unchecked “Show only subscribed folders” then exited and restarted Thunderbird, then she could empy Trash. I hope this helps. You can also always view Inbox Trash in the DreamHost webmail interface.
Glitch?: DreamHost’s Email disk usage warning overview help says “DreamHost purges all spam and trash email messages after 15 days.” But our Trash and Spam folders have messages much older than this contributing to our disk space, going back to October 14. It is November 10, so that’s 26 days.