SMTP: FAQs & Troubleshooting
Troubleshoot SMTP related issues on Netcore CPaaS dashboard.
Common SMTP Errors and Troubleshooting
Refer to the given table to know the errors you may encounter.
| Error Message | What It Means | How to Fix It |
|---|---|---|
Authentication failed | Username/password are incorrect or not provided | Check credentials in Netcore settings; ensure you use full correct username; reset password if needed. ([Netcore CPaaS User Guide][2]) |
Sender address rejected: not logged in | You're trying to send from a sender address that isn’t allowed | Use a sender email from a domain verified in Netcore account. ([Netcore CPaaS User Guide][2]) |
Client host rejected | SMTP server is rejecting the sending IP or client | Ensure that your IP isn't blocked; if using IP binding, ensure configuration is active; check network/firewall settings. |
Relay access denied | Authentication not done properly, or trying to relay from unauthorized location | Ensure your app is correctly authenticating; check library settings; verify sender domain. |
Unable to connect to host / Timeout | Network/firewall issues, wrong port, or encryption mismatch | Check that firewall allows outgoing TCP on 25, 587, or 2525; try alternate port; verify SSL/TLS settings. |
TLS handshake failed | Encryption mismatch or invalid certificate | Verify certificate chain; use correct encryption method (STARTTLS vs SSL); ensure system date/time is correct. |
FAQs
Q: Can I use port 465 with Netcore SMTP?
A: If Netcore supports SSL on port 465, yes. Otherwise, use ports 587 or 2525 with TLS/STARTTLS. (Current documentation shows ports 25, 2525, and 587 with TLS.)
Q: Do I need to verify my sending domain?
A: Yes. If your sender domain is not verified or active in your Netcore account, sending may fail.
Q: Can I send from multiple domains?
A: Yes. You can add and verify multiple sending domains. Use whichever verified domain suits your "From" address.
Q: What are the rate limits or throughput limits?
A: Rate limits depend on your plan. For example, you may have a limit of X emails per minute or per hour. If limits are not published, contact Netcore support for clarification.
Q: What happens if my IP is blacklisted?
A: If you are using a shared IP, your reputation may be affected by other senders. Dedicated IP binding can help. Monitor bounce and spam rates, and follow best practices for content, headers, and domain alignment.
Q: Is SMTP more secure than API sending?
A: Both can be secure. API uses HTTPS with token authentication, while SMTP uses TLS encryption with username and password. For higher security or when avoiding legacy protocols, API sending may be preferred.
Q: Can I monitor delivery, bounce, or open events for SMTP sends?
A: Yes. Netcore provides delivery, bounce, and engagement reporting for SMTP sends, as long as your domains are verified and tracking is enabled.
Updated about 4 hours ago