Missend Guard for Gmail

Quietly prevents Gmail misdelivery. Warns only when something looks off: wrong recipient, look-alike address, forgotten BCC. Free.

A Gmail misdelivery-prevention extension that checks recipients and BCC before you send. Protect the emails that matter — the ones to clients and customers — from going to the wrong place, with a tool that stays quiet by default and stops you only when something looks off. It never nags. Because it doesn't force a check on every send, your normal sends go through untouched — a dialog appears only for the unusual: a first-time recipient, a look-alike address, a forgotten BCC. And nothing ever leaves your machine: the extension contains no networking code at all. The only permission it asks for is "storage," and the whole thing is open source for anyone to inspect. ■ Why it doesn't "confirm every time" When every send forces the same confirmation, the check becomes a mindless click ritual and the one message that matters slips through. Missend Guard is the opposite: it interrupts only when something is off, so the dialog appearing is itself the signal that something is wrong. ■ The near-misses it stops before you send • Forgotten BCC — stops a blast with many external addresses in To/Cc before it leaks everyone's address at once • Mix-ups — catches "Saito" picked instead of "Sato," from the pattern in your sending history • Different companies mixed in — is someone from Company B in a mail meant for Company A? • Look-alike addresses / domains — flags typos like "gmial.com" • First-time recipients — catch autocomplete slips and typos on the spot • Greeting/recipient mismatch — you wrote "Dear Mr. Sato" but no Sato is among the recipients (kanji variants and romanized addresses supported) • New face in a thread — someone never part of a same-subject thread is suddenly added ■ It gets quieter the more you use it Confirmed recipients are learned, and the same confirmation never appears twice (only the BCC suggestion repeats, to prevent leaks). Within days it settles into: nothing for your usual recipients, a stop only when something feels wrong. Mistakenly learned recipients can be individually forgotten or fully erased at any time. ■ Built to be trusted — because it lives on your email • Zero external sending — nothing goes to the developer or any third party; it contains no networking code (open source: https://github.com/cysecukazch/missend-guard) • Least privilege — the only permission is "storage"; runs on mail.google.com only • Verifiable — open source (MIT License); anyone can read the code • Under your control — learning data stays in your own Chrome and can be erased anytime • Fine for company use — no external sending, storage-only permission, open source; easy to explain to an IT department • Built by a security educator — the author of an introductory information-security book published in Japan (Gijutsu-Hyoronsha). Official site: https://cysecukazch.github.io/missend-guard/ ■ Small touches • Ctrl+Enter / ⌘+Enter keyboard sends are checked too • Recipients on your own domain (internal mail) aren't checked, so casual internal mail is never interrupted (disabled on freemail accounts such as Gmail) • Learned recipients carry over to a new PC via Chrome Sync (can be turned off; display names are never synced) ■ Setup is just installing it Works out of the box with no configuration. Every check can be toggled from the toolbar icon, and the full detection spec is published on the help page. Free to use. * Gmail is a trademark of Google LLC. This extension is not endorsed by or affiliated with Google.