Hello,
Are you using Outlook on the web or the Outlook desktop app?
This issue usually relates to sync or view settings, not storage. In Outlook desktop, go to File, Account Settings, Account Settings, double click your account, then check “Mail to keep offline” and move the slider to All. In Outlook on the web, check the Deleted Items, Archive, and Junk folders, then use the search bar with “All folders” selected. Also go to Settings, Mail, Sync email and confirm your account is fully synced. If emails still do not appear, go to Deleted Items and select “Recover items deleted from this folder” to restore older messages.