What causes '503 5.5.0 polite people say HELO first' bounce errors with Ziggo.nl and how are they resolved?
Michael Ko
Co-founder & CEO, Suped
Published 16 Jul 2025
Updated 16 Aug 2025
6 min read
Receiving a '503 5.5.0 polite people say HELO first' bounce error can be perplexing, especially when you're sure your sending system is following the correct SMTP protocol. This error typically indicates a problem with the SMTP session's initial handshake, where the client is expected to introduce itself using the HELO or EHLO command.
While a 503 error generally points to an invalid command sequence, the specific message 'polite people say HELO first' implies that the receiving server, in this case, Ziggo.nl, didn't perceive the HELO/EHLO command correctly, or it encountered an issue during processing before that command could be accepted. This can lead to a sudden spike in bounce rates for a mail provider that previously accepted your emails without issue.
For email service providers (ESPs) and high-volume senders, such an error from a major ISP like Ziggo.nl can severely impact deliverability. Understanding the root cause, whether it's on your end or the recipient's, is crucial for maintaining your email sending reputation.
Understanding the '503 polite people say HELO first' error
The 503 error code in SMTP signifies an invalid command sequence or, more broadly, an issue where the server cannot process the request due to an incorrect state. The 'polite people say HELO first' addition is a specific, often human-readable, message indicating that the server expected the HELO or EHLO command to initiate the conversation.
The SMTP handshake begins with the client connecting to the server. The server responds with a 220 service ready message, and then the client must send a HELO (or EHLO for Extended SMTP) command to identify itself. If this sequence is disrupted, or if the server's configuration causes it to misinterpret a valid HELO/EHLO, this 503 error can occur. For more technical details on SMTP commands, you can refer to resources like this discussion on TechRepublic.
A client sending mail typically follows this flow:
Example SMTP conversation
220 server.example.com ESMTP service ready
HELO client.example.com
250 server.example.com Hello client.example.com, pleased to meet you
MAIL FROM:<sender@example.com>
...
The 503 5.5.0 indicates that the server did not receive the expected HELO command or received it at an inappropriate time in the sequence. This is a critical step, as it establishes the client's identity before any mail transfer commands are issued.
Common causes of 503 errors, and the Ziggo.nl context
While 503 errors often suggest issues like a server being temporarily unavailable due to maintenance or overload, the 'polite people say HELO first' variant narrows the problem down to the initial SMTP communication. It usually means something went wrong with the client's introduction or the server's ability to process it.
In the specific case of Ziggo.nl, reports indicated that the issue stemmed from internal configuration changes. This is a common occurrence where an ISP's mail servers undergo updates or modifications that inadvertently affect their ability to correctly parse or respond to standard SMTP commands for a brief period. Such glitches are usually resolved quickly by the ISP.
This type of error differs from other common bounce messages like a 550 relaying denied or 550 invalid domain error, which are often related to recipient policies or domain validity. A 503 HELO error points directly to a protocol-level communication breakdown during the initial connection.
Typical server-side causes
Maintenance or updates: The server is temporarily down or reconfiguring.
Overload: The mail server is experiencing unusually high traffic.
Configuration glitches: As with Ziggo.nl, internal software changes can disrupt normal operation.
Troubleshooting steps and server-side resolution
When encountering a '503 5.5.0 polite people say HELO first' bounce, your first step is to verify your own sending logs. Ensure that your mail server or ESP is indeed sending the HELO or EHLO command correctly and at the right stage of the SMTP session. You can confirm this through your mail server logs, which record the full SMTP conversation.
If your logs confirm that the HELO/EHLO command is being sent as expected, the issue is almost certainly on the recipient's side. In such cases, the best approach is to monitor the situation. Temporary server issues, like the configuration hiccup at Ziggo.nl, often self-resolve within a short period, typically minutes to a few hours.
If the problem persists, it may be necessary to contact the recipient's postmaster or abuse desk with detailed logs of your attempted connections. This provides them with the information they need to diagnose and fix any ongoing issues on their end. Meanwhile, you might see soft bounces from the affected domains, which require continued monitoring and retry attempts.
Your mail server (client) checks
Review logs: Confirm that your system sends HELO/EHLO at the start of the SMTP session.
Check network connectivity: Ensure no firewalls or network settings are blocking the initial communication.
Recipient mail server (ISP) considerations
Temporary configuration issues: Often self-correcting after a short period.
Overload or maintenance: Can cause intermittent protocol errors. You might also encounter general 503 HTTP errors in web contexts, though the underlying cause for email is different.
Best practices for senders
While immediate resolution for a 503 HELO error from an ISP like Ziggo.nl often lies with the ISP fixing their internal systems, senders can implement best practices to minimize the impact of such issues and maintain strong email deliverability.
Ensure your sending infrastructure strictly adheres to SMTP RFCs (Request for Comments) for all commands, including HELO/EHLO. This includes providing a valid domain in your HELO/EHLO command, which often matches your reverse DNS (rDNS) or sending domain. Also, consistently monitoring your email domain reputation and IP reputation helps in the long run. Even if the error is due to a glitch, a good reputation can sometimes facilitate quicker recovery.
Additionally, a robust retry mechanism for temporary bounce errors is vital. A 503 error is typically transient, meaning that retrying the send after a delay is often successful once the recipient server's issue is resolved. You should also regularly check if your sending IPs are on any email blocklists (or blacklists), as being listed could also indirectly affect server responsiveness or lead to other bounce types.
Final thoughts on email deliverability
The '503 5.5.0 polite people say HELO first' bounce error with Ziggo.nl highlights the occasional, unpredictable nature of email deliverability. While often frustrating, these errors are typically temporary and stem from an ISP's internal system adjustments.
For senders, maintaining precise SMTP protocol adherence, closely monitoring bounce logs, and having a robust retry strategy are key. These practices ensure that you are prepared for such transient issues and can quickly confirm whether the problem lies with your setup or the receiving server.
Ultimately, patience and clear communication with affected ISPs, when necessary, will resolve these temporary deliverability hiccups, allowing your emails to reach their intended recipients without prolonged disruption.
Views from the trenches
Best practices
Ensure all outgoing mail servers strictly adhere to the SMTP protocol and send a valid HELO/EHLO command first.
Maintain comprehensive logging of SMTP conversations to easily diagnose communication issues.
Implement robust retry mechanisms for temporary bounce errors, including appropriate delays.
Keep your domain and IP reputation strong through consistent good sending practices.
Common pitfalls
Ignoring 503 errors and assuming they are always recipient-side, without checking your own logs.
Not having a retry policy for temporary errors, leading to missed delivery opportunities.
Failing to monitor deliverability trends and noticing sudden spikes in bounce rates from specific ISPs.
Sending HELO/EHLO with an invalid or generic domain name.
Expert tips
Actively participate in email deliverability communities to share and receive insights on ISP-specific issues.
Establish a direct communication channel with major ISPs where possible for faster resolution of widespread issues.
Utilize DMARC reports to gain deeper insights into authentication failures, which can sometimes precede deliverability issues.
Regularly check your blacklists (or blocklists) for any listings that might affect server responses.
Marketer view
Marketer from Email Geeks says they noticed over six different ESPs experiencing these bounces to Ziggo.nl, which was unusual for a provider they send to daily.
2022-07-29 - Email Geeks
Expert view
Expert from Email Geeks says they confirmed their connections were indeed sending HELO first, ruling out client-side protocol violation.
Ziggo.nl, reports indicated that the issue stemmed from internal configuration changes. This is a common occurrence where an ISP's mail servers undergo updates or modifications that inadvertently affect their ability to correctly parse or respond to standard SMTP commands for a brief period. Such glitches are usually resolved quickly by the ISP.
