The .mbx extension is used by which email client?

• A. Eudora
• B. Outlook Express
• C. Gmail
• D. Mozilla Thunderbird

Answer: (A)

The .mbx extension points to how Eudora stored its email. In Eudora, each mailbox was saved as a single file with the .mbx extension (often alongside a companion .toc index file). This makes .mbx a recognizable artifact for Eudora. In contrast, Outlook Express uses .dbx files for mailboxes, Gmail is a cloud-based service with no local .mbx files, and Mozilla Thunderbird uses the mbox format where mailbox files typically have no extension or use the mailbox name without an .mbx suffix. So, the .mbx extension is most closely tied to Eudora.