How to resolve Ziggo rate limiting issues for email senders?
Michael Ko
Co-founder & CEO, Suped
Published 23 Jul 2025
Updated 15 Aug 2025
6 min read
Dealing with email rate limiting can be frustrating, especially when it comes from a major internet service provider like Ziggo in the Netherlands. If your emails to Ziggo, or its associated domains like home.nl, upcmail.nl, casema.nl, and chello.nl, are being delayed or deferred, you're likely encountering their rate limiting policies. This often manifests as a deferral message similar to 421 4.1.1 MXIN503 Hourly ratelimit for your IP exceeded.
These limits are put in place by mailbox providers to protect their users from spam and to manage server load. While they can be a nuisance for legitimate senders, understanding the underlying causes and implementing the right strategies can help you resolve these issues and improve your email deliverability.
Understanding Ziggo's email policies
Ziggo, like many other large internet service providers, employs robust anti-spam measures, which include rate limiting. This means they limit the number of emails an IP address can send to their network within a specific timeframe, such as an hour. The goal is to prevent a single sender from overwhelming their systems or delivering a large volume of unwanted messages.
These limits are often dynamic, adjusting based on your sending reputation. A good sending reputation allows for higher sending volumes, whereas a poor one can quickly trigger aggressive rate limits or even lead to a blocklist (blacklist) entry. It's their way of temporarily throttling suspicious or low-reputation senders to ensure a better experience for their users.
A key factor for Ziggo is their reliance on third-party spam filtering solutions, particularly Cloudmark. If Cloudmark identifies suspicious patterns or active spam fingerprints from your sending IP or domain, Ziggo will likely reduce the number of messages it accepts from you. This can result in significant throttling even if you don't see direct blocklist entries elsewhere, as the system proactively tries to prevent potential abuse. Issues related to rate limiting for excessive data use, which Cloudmark might detect, can also trigger these responses.
Diagnosing the root causes
When you face Ziggo rate limiting, the first step is always thorough diagnosis. It's rarely a simple, isolated issue. The goal is to pinpoint what aspects of your sending behavior or email configuration might be triggering these limits.
Examine your bounce logs carefully. While Ziggo's deferral message gives you a clear indication of hourly rate limits, it doesn't tell you why these limits have been imposed on you. Look for patterns in other bounce types or indicators of poor recipient quality.
Your overall sender reputation is paramount. High spam complaint rates, low engagement metrics (like open or click-through rates), or hitting spam traps can severely degrade your reputation, leading to stricter rate limits. Use tools like Google Postmaster Tools to get insights into your domain's reputation with major mailbox providers.
Common rate limit triggers
Poor sender reputation: Consistent low engagement or high complaint rates.
Sudden volume spikes: Sending significantly more email than usual.
Invalid recipients: A high bounce rate due to sending to non-existent addresses.
Low inbox placement: Emails frequently landing in spam folders or not delivered.
Bounce rate spikes: An unexpected increase in hard or soft bounces.
Blocklist (blacklist) listings: Your IP or domain appearing on a public or private email blocklist.
Strategic steps to mitigate and resolve
Once you have an idea of the potential causes, you can implement a strategy to reduce the rate limiting. One of the most effective approaches is to gradually warm up your IP address and domain with Ziggo by sending small, consistent volumes of highly engaged email, then slowly increasing the volume. This builds trust and demonstrates to Ziggo that you are a legitimate sender.
Ensure your email authentication is perfectly configured. This includes SPF, DKIM, and DMARC records. Proper authentication proves that your emails are legitimate and haven't been spoofed, which is a major trust signal for mailbox providers like Ziggo.
Aggressively maintain your mailing list hygiene. Remove bounced addresses immediately and suppress unengaged subscribers. Sending to invalid or inactive email addresses not only wastes resources but also signals to ISPs that your list quality is poor, which can lead to further rate limiting or blocklisting (blacklisting).
Key technical checks
Beyond general best practices, ensure your DNS records are correctly set up and align with your sending practices. Misconfigurations can lead to authentication failures and contribute to reputation issues.
Actively monitor your email performance metrics, including bounce rates, complaint rates, and engagement. Pay close attention to your DMARC reports, which can provide invaluable insights into authentication failures and potential deliverability issues across various mailbox providers, including Ziggo. This proactive monitoring allows you to identify and address problems before they escalate.
Finally, communicate with Ziggo. While contact routes can sometimes feel unresponsive, reaching out to their abuse or postmaster team at abuse@ziggo.nl or via their official spam support page can sometimes provide clarity or even lead to whitelisting if your sending practices are solid.
Long-term deliverability best practices
Resolving a specific rate limiting issue is one thing, but maintaining excellent email deliverability is an ongoing process. Consistent monitoring of your sender reputation, bounce rates, and feedback loops is essential.
Focus on sending content that your subscribers genuinely want to receive. High engagement rates signal to ISPs that your emails are valued, which positively impacts your reputation and can help prevent future rate limiting. Regularly review your email deliverability tests to catch problems early.
Category
Action
Impact
Volume & Consistency
Start small and gradually increase sending volume.
Builds trust and avoids sudden flags.
Authentication
Implement and monitor SPF, DKIM, and DMARC.
Verifies sender identity, reduces spoofing risk.
List Hygiene
Regularly remove invalid or unengaged subscribers.
Lowers bounce rates and spam trap hits.
Content Quality
Send valuable, relevant content to engaged users.
Increases engagement, reduces complaints.
Views from the trenches
Best practices
Maintain consistent sending volumes to avoid sudden spikes that trigger rate limits.
Prioritize email list hygiene by regularly removing inactive and invalid addresses.
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and monitored.
Segment your audience and tailor content to improve engagement and reduce complaint rates.
Contact Ziggo's abuse or postmaster team for specific guidance and potential delisting.
Common pitfalls
Ignoring early signs of rate limiting or deferrals, allowing issues to escalate.
Sending to outdated or unengaged lists, leading to high bounce and complaint rates.
Failing to implement or properly configure email authentication, undermining sender trust.
Expecting immediate resolution from ISPs without demonstrating improved sending practices.
Not monitoring external blocklists (blacklists) or Cloudmark flags that influence deliverability.
Expert tips
Use a methodical approach to diagnose rate limiting, reviewing all bounce messages for clues.
Leverage postmaster tools from major ISPs to monitor your sending reputation proactively.
Implement a gradual IP warming strategy for new IPs or when increasing sending volume.
Consider seeking direct contact with Ziggo's postmaster team if standard routes are unresponsive.
Continuously analyze engagement metrics to adjust sending strategies and content.
Marketer view
Marketer from Email Geeks says they started experiencing heavy rate limiting from Ziggo last week and found their usual postmaster/abuse contact routes unresponsive, prompting them to seek advice.
2020-11-02 - Email Geeks
Expert view
Expert from Email Geeks says they could try sharing specific recipient domains to help diagnose the issue.
2020-11-02 - Email Geeks
Restoring your email sending to Ziggo
Resolving Ziggo rate limiting requires a combination of immediate troubleshooting and long-term strategic adjustments to your email program. By meticulously reviewing your sending practices, ensuring robust authentication, maintaining pristine list hygiene, and engaging responsibly with your subscribers, you can steadily improve your sender reputation.
Remember, email deliverability is an ongoing effort. Consistent adherence to best practices will not only help you overcome current rate limiting issues with Ziggo but also safeguard your sending health across all major mailbox providers, ensuring your messages consistently reach the inbox.
