What causes '503 5.5.0 polite people say HELO first' bounce errors with Ziggo.nl and how are they resolved?

7 Marketer opinions 3 Expert opinions 4 Technical articles 1 Resource

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
7Marketer 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.

February 2025 - 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.

December 2021 - Email Geeks

Marketer view

Email marketer from MXToolbox explains that the 503 error is a generic error which means the server has refused the connection because it thinks you have contravened something. You should check the logs as this will tell you what the issue is.

March 2024 - MXToolbox

Marketer view

Email marketer from EmailOnAcid says that you should use a 'telnet' command to test the connection to the server - this will confirm if there is a error in the authentication process of your emails.

August 2024 - EmailOnAcid

Marketer view

Email marketer from StackOverflow answers that the typical SMTP sequence should be: connect, HELO/EHLO, MAIL FROM, RCPT TO, DATA, and QUIT. A 503 error suggests a deviation from this sequence.

May 2021 - StackOverflow

Marketer view

Email marketer from Postmark shares that you can review your servers logs or contact the recipient to get their logs - as this will show you why the email was blocked.

April 2024 - Postmark

Marketer view

Email marketer from Reddit shares that a 503 error might occur if the sending server's IP address is blacklisted or experiencing temporary network issues, preventing proper communication during the initial HELO/EHLO handshake.

April 2024 - Reddit

What the experts say
3Expert 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.

July 2021 - 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).

April 2024 - Spamresource.com

Expert view

Expert from Wordtothewise.com explains that the HELO/EHLO should accurately reflect your server's identity and sending reputation. Inconsistent or misleading HELO information can lead to deliverability problems and 503 errors.

February 2024 - Wordtothewise.com

What the documentation says
4Technical 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.

June 2021 - 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.

September 2022 - RFC Editor

Technical article

Documentation from cPanel states that you should check your email client settings and also check your cPanel settings. You may have too many emails being sent at once, which causes the receiving server to block you. To resolve, slow down the amount you send.

December 2022 - cPanel

Technical article

Documentation from Microsoft Learn explains that a 5xx SMTP error code signifies a permanent error. Specifically, 503 means 'Bad sequence of commands' and suggests the client sent commands out of order, which can include HELO.

December 2024 - Microsoft Learn