We built Mailtester.ai to see if your emails actually land in the inbox

TL;DR: I’m a designer, my friend’s a full-stack dev. We created an early beta of Mailtester.ai

At a one day app-building event. Basically a full-day coding plus vibe coding. Send a test email to a unique address and instantly get AI + technical analysis (spammy phrasing, link reputation, SPF/DKIM/DMARC, etc.).

Quick tests work without signup. Register, and you get a workspace with a full history of all your emails.

The problem we wanted to solve? You never really know where your emails end up: spam, promotions tab, or the real inbox. And sometimes they even look like a phishing email from 2012.

So we built Mailtester.ai

• Copy a unique test address

• Send your email there

• Get instant AI feedback (spam triggers, content tips, link rep) + a full technical breakdown (DKIM, SPF, DMARC, SpamAssassin)

On the dev side the main tool we used was Cursor to speed up the coding. The rest were more classic tools like Figma, ChatGPT, Perplexity, etc.

It’s still an early beta, but we’re already using it on our own campaigns and feedback from some people so far has been positive.

Would love any comments or ideas. Or just try it out on that newsletter you’re never sure is reaching anyone.