Troubleshooting SMTP Errors
Decode the error messages your mail server returns and fix the underlying cause.
When a test or a send fails, Vecta stores the server's exact response on the SMTP config and on the individual send record. That text is the fastest route to the cause.
Authentication errors
| Message | Cause | Fix |
|---|---|---|
| 535 Authentication failed | Wrong password, or provider requires an app password | Generate an app password (Gmail, Outlook) and use that |
| 534 / 5.7.9 application-specific password required | 2FA is on | Create an app password |
| Username and Password not accepted | Username isn't the full address | Use the complete email address |
Connection errors
| Message | Cause | Fix |
|---|---|---|
| Connection timeout | Wrong host/port, or outbound SMTP blocked | Verify host spelling; try 587, then 465 |
| ECONNREFUSED | Nothing listening on that port | Wrong port for this provider |
| self-signed certificate / hostname mismatch | Host doesn't match the certificate | Use the exact host your provider documents |
Rejection errors
| Message | Cause | Fix |
|---|---|---|
| 550 relay access denied | From address isn't owned by the authenticated mailbox | Set From to your real address |
| 553 sender address rejected | Same as above, phrased differently | Match From to the mailbox |
| 552 message too large | Body exceeds the server limit | Shorten the email; avoid embedding images |
| 421 too many messages | You're sending too fast | Lower your per-minute and per-second caps |
These never suppress your contacts
Everything above is a problem on your side, so Vecta records the send as failed but leaves the contact untouched. Only a genuine recipient rejection marks someone as bounced.
A repeatable checklist
- 1Open the SMTP config and read the stored error text.
- 2Press Test to reproduce it on demand.
- 3Confirm the username is the full email address.
- 4Try port 587, then 465.
- 5Confirm the From address matches the mailbox.
- 6If the provider uses 2FA, regenerate the app password.
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Related articles
SMTP Setup Guide
Connect your mailbox to Vecta: what each field means, which port to use, and how to set safe sending limits.
Gmail SMTP Setup
Step-by-step setup for Gmail and Google Workspace, including creating the App Password Google requires.
Understanding Bounce Handling
What a bounce really is, how Vecta tells a dead address apart from your own broken settings, and why that matters enormously.