Transmit - Free sandbox email API. Credits that roll over.

Most email APIs make you verify a domain before you can really test. Your first “test” is already a send. Transmit starts in a free sandbox: separate keys, simulated email, real webhooks. Sandbox keys never send — like Stripe. No domain to start. When you’re ready: subscribe, verify domain, create a live key. Same API. Real delivery. $20/mo adds 30,000 emails. Unused credits roll over. No tiers. No midnight reset. Build first. Send when you’re ready. transmit.dev