Why are emails bouncing when sending to Tiscali.it and how to solve it?
Michael Ko
Co-founder & CEO, Suped
Published 11 May 2025
Updated 15 Aug 2025
8 min read
If you're experiencing high bounce rates when sending emails to Tiscali.it, you're not alone. Many senders, particularly those running bulk marketing campaigns, encounter significant challenges with this Italian Internet Service Provider (ISP). A common and frustrating bounce message you might see is smtp;421 4.2.1 Service not available. This error indicates that Tiscali's mail servers are refusing the connection, often due to issues on their end or how your sending infrastructure interacts with their specific policies.
Understanding the root causes of these bounces is crucial for improving your email deliverability. While generic email bounce reasons like invalid addresses or content issues can always play a role, Tiscali.it often presents unique infrastructure and policy-related hurdles that require specific attention. It's not always about typical spam filtering but rather technical connectivity challenges.
When you send a large volume of emails, especially to a domain like Tiscali.it, you might encounter situations where a significant portion of your mail, sometimes over 50%, is bounced. This can happen even if you use multiple IP addresses, as the problem might lie with the recipient's mail exchange servers or their specific handling of incoming mail.
We will explore why these specific bounces occur and provide actionable steps to help you overcome these challenges and significantly improve your inbox placement rates when sending to Tiscali.it.
Understanding the common Tiscali.it bounce error
The primary cause of the 421 4.2.1 Service not available bounce from Tiscali.it often points to issues with their Mail Exchange (MX) servers. Specifically, it has been observed that some of their backup MX servers might be unresponsive or dead. When your mail server attempts to deliver an email, it queries DNS for the recipient domain's MX records, which list the mail servers responsible for accepting mail for that domain, along with their priority. If it tries to connect to an unresponsive server, it results in a bounce.
Tiscali.it's MX records typically show a hierarchy of servers. While lower-priority servers are meant as backups, some mail sending systems might still attempt to connect to them, or encounter issues if higher-priority servers are slow. The Service not available error directly reflects this inability to establish a successful connection.
Beyond dead servers, the problem can also stem from slow response times from Tiscali's operational MX servers. If your Mail Transfer Agent (MTA) has a low connection timeout configured, it might prematurely abandon the connection attempt, leading to a bounce even if the server would eventually respond. This situation can be particularly problematic for high-volume senders, as the cumulative effect of these timeouts can lead to a large number of bounced emails. It's similar to other ISPs that might have specific connection requirements, as seen when sending to other Italian providers.
The impact of Tiscali.it's server and greylisting policies
Tiscali.it, like many other ISPs, employs greylisting as a spam prevention technique. Greylisting works by temporarily rejecting emails from unknown senders, requiring the sending server to try again after a short delay. A legitimate sending server will retry the delivery, while most spam bots will not. While effective against spam, this mechanism adds a layer of complexity for legitimate senders, especially when combined with slow server responses.
The challenge arises when your MTA's retry logic and timeouts are not configured to accommodate Tiscali's greylisting. If your server gives up too quickly, the email will bounce even though Tiscali's server intends to accept it on a later retry. This is a common pattern for ISPs that are very protective of their inboxes, similar to how AOL and Yahoo manage inbound mail. Understanding and configuring for greylisting is essential for consistent deliverability.
Beyond greylisting, Tiscali.it likely employs internal rate limits. Sending a very large volume of emails within a short period from a single IP address, even if it's legitimate mail, can trigger these limits, resulting in temporary rejections or bounces. While using multiple IPs can help distribute the load, if your overall sending volume to Tiscali is too high for their systems to handle, you will still see bounces. It's crucial to scale your sending gradually and adjust your hourly throttling to match their capacity.
Server response vs. sending configuration
While Tiscali's infrastructure issues are a factor, your server's configuration plays a critical role in how it reacts to these challenges. Misconfigured timeouts or retry settings can exacerbate the problem, turning temporary rejections into hard bounces.
Ensuring your email infrastructure is optimized for Tiscali.it
Optimizing your MTA's configuration is paramount when dealing with ISPs like Tiscali.it that have spotty response times or employ greylisting. The default timeout settings on many MTAs might be too aggressive, leading to premature disconnects. You should consider increasing the connection timeout and the wait time for initial SMTP responses.
Beyond timeouts, adjust your retry schedule to be more patient. For example, instead of giving up after a few minutes, allow for longer intervals between retries, especially for greylisted responses. This ensures that your server can successfully complete the delivery handshake when Tiscali's servers are ready to accept the mail. This approach aligns with best practices for handling greylisting effectively.
Another crucial aspect is managing your sending volume to Tiscali.it. Implementing specific hourly throttles for this domain can prevent you from hitting their internal rate limits. Instead of blasting 100,000 emails at once, spread them out over several hours or even days. This gradual approach signals to Tiscali that you are a legitimate sender and helps avoid reputation-based blocking (or blacklisting). Also, ensure you have proper DNS records, like PTR records, as missing PTR records can also cause bounces.
Strategies for maintaining healthy deliverability to Tiscali.it
While technical configurations are vital, maintaining a strong sender reputation is always fundamental for email deliverability, especially with ISPs that have stricter filtering. This means adhering to best practices like sending only to engaged recipients, maintaining a clean email list, and promptly removing invalid or inactive addresses. A poor sender reputation can lead to being added to an email blocklist (or blacklist), which significantly impacts your ability to reach inboxes.
Regularly monitor your email sending metrics, including bounce rates, complaint rates, and open rates, specifically for Tiscali.it domains. High bounce rates to Tiscali.it, even if temporary, should prompt a review of your sending practices and configurations. Similarly, a spike in complaint rates can signal content issues or list fatigue.
Always ensure your email authentication records, such as SPF, DKIM, and DMARC, are correctly configured. ISPs use these records to verify the legitimacy of incoming mail. While they might not directly resolve Service not available errors, they contribute significantly to your overall sender reputation and can prevent other deliverability issues. Consistent authentication is key for boosting deliverability rates across the board.
Views from the trenches
Best practices
Maintain meticulous list hygiene to ensure you are only sending to active and engaged Tiscali.it recipients.
Adjust MTA connection timeouts and retry schedules to be more patient with Tiscali's greylisting and slow server responses.
Implement specific hourly throttling for Tiscali.it email volume to avoid hitting their internal rate limits.
Continuously monitor bounce logs for specific error messages to understand the real-time status of Tiscali's servers.
Ensure all email authentication protocols, including SPF, DKIM, and DMARC, are correctly implemented and aligned.
Common pitfalls
Ignoring the 'Service not available' error, assuming it's a temporary glitch without investigating underlying causes.
Using default MTA settings that have aggressive timeouts, leading to bounces from greylisted mail.
Sending excessively high volumes of email to Tiscali.it in short bursts, triggering their rate limits.
Failing to track bounce codes accurately, which prevents effective troubleshooting of Tiscali-specific issues.
Neglecting to monitor Tiscali's MX records for changes or prolonged outages that could impact delivery.
Expert tips
Use a telnet command to manually check connectivity to Tiscali's MX servers to diagnose live server issues.
Consider segmenting your Tiscali.it recipient list and sending smaller batches at optimized times.
Engage with Tiscali's postmaster if possible, providing specific details of your bounce errors and sending patterns.
Analyze your DMARC reports for insights into Tiscali's handling of your authenticated mail streams.
Diversify your sending infrastructure if Tiscali continues to be a persistent challenge.
Marketer view
A marketer from Email Geeks mentioned they were experiencing many bounces from different bulk marketing campaigns to Tiscali.it and found it strange, suspecting a blacklist.
2021-02-23 - Email Geeks
Marketer view
An expert from Email Geeks pointed out that Tiscali's low priority MX server appeared to be dead, which could cause significant issues for email delivery.
2021-02-23 - Email Geeks
Summary of solutions
Dealing with Tiscali.it email bounces requires a blend of technical adjustments and adherence to fundamental email deliverability best practices. The 421 4.2.1 Service not available error points to specific issues with their MX servers and how your MTA interacts with them. By understanding Tiscali's greylisting and potential infrastructure weaknesses, you can tailor your sending strategy to improve success.
The key is patience in your MTA configuration, strategic throttling of your mail flow, and diligent monitoring of your sender reputation and bounce logs. While Tiscali.it can be a challenging recipient, proactive adjustments can significantly reduce bounce rates and ensure your important messages reach their intended inboxes.
Remember that consistent success in email deliverability, especially to ISPs with unique challenges, is an ongoing process. Regularly review your email performance, adapt your sending practices, and stay informed about ISP policies to maintain high inbox placement rates. These steps are crucial for overall email deliverability in 2025 and beyond.
