Summary
The '503 5.5.0 polite people say HELO first' error arises from issues during the initial SMTP handshake, primarily related to the HELO/EHLO command. These issues can stem from server-side problems (like configuration hiccups), client-side misconfiguration, or network-related disruptions. Key causes include incorrect SMTP sequence (HELO/EHLO not first), malformed HELO/EHLO format (invalid domain, missing FQDN, IP mismatch), server blacklisting, or temporary network issues. Experts emphasize the importance of a valid, resolvable HELO/EHLO hostname matching the sending server's IP and accurately reflecting its identity/reputation. Resolution steps include checking server logs, verifying the SMTP sequence, ensuring a valid HELO/EHLO format, testing connectivity via telnet, contacting the recipient, and reviewing email client/cPanel settings.
Key findings
- SMTP Sequence: The HELO/EHLO command must be the first command after connecting in the SMTP sequence.
- HELO/EHLO Format: The HELO/EHLO must be a valid, resolvable FQDN aligning with the sending server's IP.
- Server Issues: Receiving server configuration problems or blacklisting can cause the error.
- Network Issues: Temporary network disruptions can interfere with the HELO/EHLO handshake.
- General Error: 503 errors are generic and indicate a rule has been broken on a server.
Key considerations
- Check Logs: Examine both sending and receiving server logs for detailed error information.
- Validate HELO/EHLO: Ensure the HELO/EHLO hostname is valid, resolves correctly, and matches the sending IP.
- Test Connectivity: Use telnet to test connectivity to the mail server and verify the HELO/EHLO exchange.
- Review Settings: Verify email client and cPanel settings, paying attention to SMTP configurations.
- Monitor Reputation: Maintain a positive sending reputation to avoid blacklisting issues.
- Contact Recipient: Reach out to the recipient's admin for assistance in troubleshooting and gaining log insights.
What email marketers say
7 marketer opinions
The '503 5.5.0 polite people say HELO first' bounce error indicates a problem with the SMTP HELO/EHLO handshake, often due to the client not sending the HELO/EHLO command first or sending it incorrectly. Causes range from server configuration issues (like Ziggo.nl's config conversion hiccup), deviations from the standard SMTP sequence, blacklisted IPs, network issues, or a malformed HELO/EHLO string (e.g., not a resolvable domain). Resolution strategies include checking server logs, verifying the SMTP sequence, ensuring a valid HELO/EHLO format, using telnet to test connectivity, and contacting the recipient to check their logs.
Key opinions
- SMTP Sequence: A 503 error often means the HELO/EHLO command wasn't the first command sent after connecting.
- HELO/EHLO Format: The HELO/EHLO hostname must be a valid, resolvable FQDN that matches the sending IP.
- Blacklisting/Network: The sending server's IP might be blacklisted or experiencing network issues.
- Generic Error: Error 503 is a general error indicating the server thinks you have contravened some rule.
- Configuration Issues: Receiving server might have configuration problems (e.g., Ziggo.nl config conversion).
Key considerations
- Check Logs: Review both your server's and the recipient's server logs for detailed error information.
- Verify SMTP Sequence: Ensure your email client or sending script follows the correct SMTP command sequence (HELO/EHLO, MAIL FROM, RCPT TO, DATA, QUIT).
- Test Connectivity: Use telnet to test the connection to the mail server and verify the HELO/EHLO handshake.
- Contact Recipient: If possible, contact the recipient's email administrator to investigate the issue on their end.
- HELO/EHLO configuration: The HELO/EHLO should accurately reflect your server's identity and sending reputation.
Marketer view
Email marketer from Email Geeks reports that Ziggo.nl confirmed they had an issue converting some configs and it is now resolved.
16 May 2022 - Email Geeks
Marketer view
Email marketer from Email Geeks shares that there were bounce issues related to ziggo.nl with the error message '503 5.5.0 polite people say HELO first' across multiple ESPs. The issue occurred roughly between 10:20am - 10:50am NL time.
18 May 2022 - Email Geeks
What the experts say
3 expert opinions
Experts emphasize the importance of a correctly configured HELO/EHLO for avoiding '503 5.5.0 polite people say HELO first' errors. The HELO/EHLO should be a valid, resolvable domain name that aligns with the sending server's IP address and reflects its identity and reputation. Using generic or mismatched hostnames, or failing to use a fully qualified domain name (FQDN), can trigger these errors and impact deliverability.
Key opinions
- Valid HELO/EHLO: The HELO/EHLO hostname must be a valid and resolvable domain name.
- IP Resolution: The HELO/EHLO hostname should resolve to the sending server's IP address.
- FQDN Requirement: The HELO/EHLO should be a fully qualified domain name (FQDN).
- Reputation Alignment: The HELO/EHLO should accurately reflect the server's identity and sending reputation.
Key considerations
- Verify Hostname: Ensure the HELO/EHLO hostname is correctly configured and resolves properly.
- Match IP: Confirm that the HELO/EHLO hostname resolves to the sending server's public IP address.
- Reputation Management: Maintain a consistent and accurate HELO/EHLO to support a positive sending reputation.
Expert view
Expert from Spamresource.com explains that ensuring your HELO/EHLO is a valid, resolvable domain name is crucial. Using a generic hostname or one that doesn't match your sending domain can trigger 503 errors.
13 Jun 2023 - Spamresource.com
Expert view
Expert from Spamresource.com shares that some providers are picky about the HELO/EHLO format. The hostname should resolve to the IP address you're sending from and be a fully qualified domain name (FQDN).
18 Jan 2022 - Spamresource.com
What the documentation says
4 technical articles
Documentation sources agree that a '503 5.5.0' SMTP error indicates a fundamental problem with the sequence of commands sent by the email client. Specifically, the HELO/EHLO command is either missing, out of order (should be the first after connecting), badly formed, or the server is expecting a different command. cPanel documentation notes that sending too many emails simultaneously can also trigger this error.
Key findings
- Command Sequence: 503 errors indicate a 'Bad sequence of commands' in the SMTP conversation.
- HELO/EHLO Priority: HELO/EHLO MUST be the first command after establishing a connection.
- Malformed HELO/EHLO: The HELO/EHLO command itself could be improperly formatted.
- Rate Limiting: Sending too many emails at once can trigger 503 errors due to rate limiting.
Key considerations
- Review SMTP flow: Double-check the sequence of commands being sent by your email client/server.
- Inspect HELO/EHLO Format: Ensure HELO/EHLO command is correctly formed and contains a valid hostname.
- Check Client Settings: Verify email client configuration, especially settings related to SMTP.
- Adjust Sending Rate: If sending bulk emails, try reducing the sending rate to avoid triggering rate limits.
Technical article
Documentation from Exim Wiki states that a 503 error can be thrown when the server expects another command but doesn't receive it. Also can occur when the HELO/EHLO is badly formed and cant be passed.
5 Oct 2024 - Exim Wiki
Technical article
Documentation from RFC Editor clarifies that the HELO or EHLO command must be the first command sent by the SMTP client after establishing a connection. A 503 error would occur if this command is missing or sent out of sequence.
12 Feb 2025 - RFC Editor
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