The Hot badge and reply detection.

Gmail's proxy re-fetches images on its own schedule, so raw 're-open' counts are noise on every tracker. Instead of pretending otherwise, MailViewed surfaces a Hot badge only on signals a machine can't fake:

• A reply — the recipient wrote back in the thread (detected by the extension in your own Gmail; the reply's content is never read or stored, just the fact and time).
• A real click on a tracked link.
• A separate reading session — they came back to your email later, beyond Gmail's background refresh window.

Hot appears on the activity list and the email's page, and a reply also lands in your notifications — so the emails worth following up on rise to the top by themselves.