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KumoMTA SMTP test — listeners, STARTTLS, and AUTH PLAIN

Test KumoMTA SMTP submission on port 587 or 25. Configure start_esmtp_listener, smtp_server_auth_plain, and verify injection with a live transcript.

1 min read Credentials redacted No signup

Connection settings

Host
your-kumo-hostname.example.com
Port
587
Security
STARTTLS

KumoMTA is a high-performance MTA configured in Lua. Unlike Gmail, there is no fixed hostname—you define ESMTP listeners with kumo.start_esmtp_listener in your init handler.

For authenticated submission, operators commonly expose port 587 with STARTTLS. KumoMTA requires AUTH on an encrypted session: implement smtp_server_auth_plain (or Vault-backed checks) and use AUTH PLAIN in clients—LOGIN is not supported.

Relay without auth is usually restricted to trusted IPs via relay_hosts on a port 25 listener. Use SMTP Tester's live transcript to confirm STARTTLS, 235 after AUTH, and a 250 queue id after DATA.

Recommended settings

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Run these settings against your SMTP server and watch the live, credential-redacted protocol transcript.

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