Mailpit vs MailTester

Mailpit is a free, open-source tool for checking email content and SMTP delivery without sending messages to real addresses. It runs a local SMTP server alongside a web interface and REST API, and is available for Linux, macOS, Windows, Docker, and self-hosted deployment. The interface displays formatted HTML, source, text, headers, raw messages, and MIME attachments with image thumbnails. Checks include HTML and link testing, message screenshots, and optional SpamAssassin scoring. The API can access, search, send, delete, tag, and release messages; messages can also be relayed, forwarded, or used to trigger configurable SMTP errors. Mailpit can send message-summary webhooks and offers a Cypress package for integration tests. The web UI and API can use HTTPS and basic authentication; SMTP supports optional authentication and TLS. By default, SMTP listens on port 1025 without encryption or authentication. Mailpit keeps the most recent 500 messages by default.

MailTester checks why email may reach spam and returns a deliverability score out of 10. To run a test, generate a disposable address, send the message there and receive a report in seconds. Scoring starts at 10, subtracts points for detected issues, and explains penalties with suggested fixes. Authentication checks include SPF, DKIM, DMARC, domain alignment, reverse DNS and forward-confirmed reverse DNS. Sending IPs are checked against Spamhaus, SpamCop, Barracuda and other DNS blocklists. Content analysis covers HTML, text-to-image ratio, links, subject, List-Unsubscribe and Message-ID. Rspamd supplies a spam score and triggered rules. Newsletter checks include one-click List-Unsubscribe under RFC 8058, message size and text-image ratio. MailTester offers web, API and self-hosted platforms. Its API creates test addresses and reads report status and scores as JSON. The free plan costs nothing, needs no account and provides 25+ checks per test.