8 guides

SMTP testing guides

Provider setup walkthroughs and troubleshooting articles for testing SMTP servers—ports, TLS, authentication, and the errors that trip people up.

Provider & MTA setup

Amazon SES SMTP test — regional endpoints and credentials Test Amazon SES SMTP using your region's email-smtp endpoint on port 587 with STARTTLS and IAM SMTP credentials. email-smtp.us-east-1.amazonaws.com · :587 · STARTTLS Read guide → Gmail SMTP test — ports, App Passwords, and troubleshooting Test Gmail SMTP (smtp.gmail.com) on port 587 or 465. Step-by-step App Password setup, STARTTLS, and how to read 535… smtp.gmail.com · :587 · STARTTLS Read guide → 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… your-kumo-hostname.example.com · :587 · STARTTLS Read guide → PowerMTA SMTP test — listeners, smtp-user, and submission on 587 Test PowerMTA (PMTA) SMTP injection. Configure smtp-listener, smtp-user, authenticated sources, STARTTLS on 587, and verify relay… your-pmta-hostname.example.com · :587 · STARTTLS Read guide → SendGrid SMTP test — apikey user and port 587 Test SendGrid SMTP at smtp.sendgrid.net:587. Use username apikey and your API key as the password. smtp.sendgrid.net · :587 · STARTTLS Read guide →

Concepts & troubleshooting

SMTP error 535 "authentication failed" — causes and fixes Fix SMTP 535 5.7.8 "username and password not accepted" / authentication failed. App passwords, API-key vs SMTP credentials,… Read guide → SMTP port 587 vs 465 — STARTTLS or implicit TLS? SMTP port 587 (STARTTLS) vs 465 (implicit TLS/SMTPS) vs 25 and 2525. Which submission port to use, how encryption differs, and… Read guide → What is an SMTP test? How online SMTP testing works What an SMTP test does: connect, EHLO, STARTTLS/TLS, AUTH, and an optional test message. Learn what each step proves and why… Read guide →