SMTP2GO test tool — mail.smtp2go.com credentials and ports

SMTP2GO is a transactional SMTP relay used by apps, WordPress sites, and small teams that want reliable outbound mail without running their own MTA. If you are configuring SMTP2GO in an app or plugin, use this SMTP2GO test tool workflow to confirm host, port, TLS, and credentials before chasing application-level errors.

Recommended settings

• Host: mail.smtp2go.com
• Port: 587 (STARTTLS) — recommended for most clients
• Alternatives: 465 (implicit TLS), 2525, 8025, 80, or 25 if your network blocks 587
• Username: an SMTP user username from the SMTP2GO dashboard (not your account login email)
• Password: the matching SMTP user password
• Auth method: Auto, PLAIN, or LOGIN
• From address: a sender you have verified in SMTP2GO

Create SMTP users (not your login password)

SMTP2GO issues per-user SMTP credentials separate from your web login:

1. Log in to the SMTP2GO dashboard.
2. Go to Settings → Users → SMTP Users (wording may appear as SMTP & API → SMTP Users).
3. Click Add SMTP user (or edit an existing user).
4. Copy the username and password shown — this pair is what your app must use.

Do not use your SMTP2GO account email and account password in SMTP clients. Forum threads with 535 authentication failed on SMTP2GO almost always mean the account password was pasted instead of an SMTP user password, or the username was truncated.

Testing with SMTP Tester

1. Host: mail.smtp2go.com, port 587, security STARTTLS.
2. Username: the SMTP user username from the dashboard.
3. Password: the SMTP user password.
4. From: a verified sender address in your SMTP2GO account.
5. To: any recipient you want to test delivery to.
6. Click Run. Look for 235 after AUTH in the transcript.

A 250 OK after DATA means SMTP2GO accepted the message for delivery. Submission success does not guarantee inbox placement — check SMTP2GO sending logs if the message does not arrive.

Port and security choices

If 587 times out, try 2525 with STARTTLS before assuming credentials are wrong.

Common errors

535 authentication failed

• Wrong username/password pair (account login instead of SMTP user).
• Extra whitespace when pasting the password.
• SMTP user disabled or deleted in the dashboard.
• Try AUTH PLAIN or LOGIN explicitly if Auto fails.

Connection timeout on 587

• Outbound 587 blocked on your network — try port 2525 or 465.
• Corporate firewall filtering SMTP — test from another network or ask IT to allow mail.smtp2go.com.

550 / 553 relay or sender rejected

• From address not verified in SMTP2GO.
• Domain DNS (SPF/DKIM) not set up — SMTP2GO may still accept the session but policy can reject later; check their sender verification UI.

TLS or certificate errors

• Match security to port: 465 needs TLS, 587 needs STARTTLS.
• For lab debugging only, you can disable Reject invalid TLS certificates in Advanced settings — never in production.

SMTP2GO vs API

SMTP2GO also offers an HTTP API for sending. The SMTP interface uses the SMTP user credentials above. API keys and SMTP user passwords are not interchangeable — if REST works but SMTP returns 535, you almost certainly have the wrong credential type in the password field.

After a successful test

• Lock in the same host, port, security, and SMTP user in your app config.
• Store credentials in environment variables or a secrets manager, not in git.
• Rotate the SMTP user password in SMTP2GO if you pasted it into a third-party support ticket.
• SMTP Tester redacts credentials from the live transcript — safe to share the output for debugging.

Related guides

• Fix 535 authentication errors
• SMTP port 587 vs 465
• SendGrid SMTP test — another transactional relay with similar port options