InboxTap is a free, open-source SMTP capture server and test SDK for signup verification, password resets, OTPs, invitations, and other email flows. Run it locally, point your app to localhost, and let your tests read the real link or code. Each test gets an isolated inbox, so parallel runs do not mix messages. Nothing is delivered externally. Works with Playwright, Vitest, Jest, Bun, and Node 20+.