MailTrail — Gmail A/B Testing

Run A/B tests on your Gmail campaigns. Up to 5 variants, open/click tracking, auto winner.

MailTrail turns Gmail into a lightweight experimentation platform — free from the makers of Experimently.ai. Compose two to five variants of a subject line and body, split your recipient list, and let MailTrail send each recipient the variant they were assigned — straight from your own Gmail account. Key features - Up to 5 variants including a control - Deterministic weighted split across recipients - Open tracking via a 1×1 pixel with proxy detection - Click tracking via signed link redirects - Reply tracking via local Gmail DOM detection (best-effort, no Gmail read scope) - Automatic winner declaration by open, click, or reply rate - Per-user pairing token — no shared credentials - Sends through the official Gmail API using your Google account Free plan limits - 500 recipients sent in the last 30 days - 10 active experiments at a time - 20 experiments per calendar month Upgrade to Experimently when you're ready to A/B test landing pages too. Privacy and permissions - gmail.send: required to send the variant messages you create - userinfo.email: used to associate sends with your dashboard account - storage: stores your pairing token and preferences locally - identity: used to authenticate you with Google OAuth - activeTab: used only when you click the toolbar button to open the MailTrail dialog - host permissions on mail.google.com, gmail.googleapis.com, www.googleapis.com, and mailtrail.experimently.ai MailTrail never reads your inbox, contacts, or existing Gmail threads through the Gmail API. Reply detection is performed locally in your browser by looking for replies to the messages MailTrail itself sent, and only the fact that a reply occurred is reported. All analytics data is scoped to your own dashboard account with row-level security.