17 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 region-specific SES SMTP credentials. email-smtp.us-east-1.amazonaws.com · :587 · STARTTLS Read guide → Brevo SMTP test: SMTP key, ports, and troubleshooting Brevo SMTP test for smtp-relay.brevo.com on port 587 with STARTTLS. Use your SMTP login and SMTP key (not the v3 API key) as… smtp-relay.brevo.com · :587 · STARTTLS Read guide → Gmail SMTP test — ports, App Passwords, troubleshooting Gmail SMTP test for smtp.gmail.com on port 587 or 465. App Password setup, STARTTLS, rate-limit errors, and how to read the… 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 and smtp_server_auth_plain, verify relay with a… your-kumo-hostname.example.com · :587 · STARTTLS Read guide → Mailgun SMTP test — domain credentials & common errors Test Mailgun SMTP at smtp.mailgun.org on port 587 with STARTTLS. Use per-domain SMTP credentials (not your API key) and read the… smtp.mailgun.org · :587 · STARTTLS Read guide → Mailjet SMTP test — API key and secret key on port 587 Test Mailjet SMTP at in-v3.mailjet.com on port 587 with STARTTLS. The username is your API key and the password is your secret… in-v3.mailjet.com · :587 · STARTTLS Read guide → Office 365 & Outlook SMTP test — ports & modern auth Office 365 and Outlook SMTP test for smtp.office365.com on port 587 with STARTTLS. Modern auth requirements, 535/550/554 fixes,… smtp.office365.com · :587 · STARTTLS Read guide → PowerMTA SMTP test — listeners, smtp-user, port 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 → Resend SMTP test: fixed username, API key, and port 465 Test Resend SMTP at smtp.resend.com on port 465 (TLS) or 587 (STARTTLS). The username is the literal string resend and the… smtp.resend.com · :465 · Implicit TLS 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 → SMTP2GO test tool: mail.smtp2go.com credentials and ports SMTP2GO test for mail.smtp2go.com with a full handshake transcript. Create SMTP users, verify your sender domain, test ports… mail.smtp2go.com · :587 · STARTTLS Read guide → SparkPost SMTP test: SMTP_Injection username and API key Test SparkPost SMTP at smtp.sparkpostmail.com on port 587 with STARTTLS. The username is SMTP_Injection and the password is an… smtp.sparkpostmail.com · :587 · STARTTLS Read guide → Zoho SMTP test — smtp.zoho.com ports & app passwords Zoho SMTP test online for smtp.zoho.com and regional hosts on port 587 with STARTTLS. App-specific passwords, sending limits,… smtp.zoho.com · :587 · STARTTLS Read guide →

Concepts & troubleshooting

SMTP authentication checker — fix error 535 Fix SMTP error 535 5.7.8 "username and password not accepted". App passwords, API-key vs SMTP credentials, username format, and… Read guide → SMTP port 587 vs 465 - STARTTLS or implicit TLS? SMTP port 587 (STARTTLS) vs 465 (implicit TLS) vs 25 and 2525. Which submission port to use, how encryption differs, and what to… Read guide → SMTP Tester vs smtper.net — free SMTP test alternative SMTP Tester vs smtper.net for testing SMTP servers. Live protocol transcript, TLS diagnostics, multiple auth methods, and privacy… Read guide → What is an SMTP test? How online SMTP testing works What an SMTP test does: connect, EHLO, STARTTLS/TLS, AUTH, MAIL FROM, RCPT TO, DATA. Annotated transcript, what each step proves,… Read guide →