GMass

GMass is a Gmail add-on that runs deliverability tests and predicts whether your email will land in Gmail's inbox, spam folder, or promotions tab. It analyzes your message against Gmail's specific filtering algorithms and provides a detailed report with an inbox placement percentage. The tool also offers email campaign tracking and scheduling features built into Gmail.

Ideal for Gmail-focused senders or those primarily targeting Gmail subscribers. The Gmail-native interface makes it simple to test before sending out your campaign. As a long-established tool with a large user base, it's proven reliable for quick deliverability checks without leaving Gmail.