Summary
Email deliverability to Tiscali.it, a major Italian internet service provider, can be challenging. Many senders experience high bounce rates, often accompanied by 421 4.2.1 Service not available errors. These issues stem from a combination of factors, including Tiscali’s specific email policies like greylisting, potential problems with their mail exchange (MX) servers, and general network congestion or slow response times.
Key findings
- Specific error code: The most commonly reported bounce message from Tiscali.it is smtp;421 4.2.1 Service not available, indicating a temporary service issue on their end.
- MX server issues: Analysis often reveals that Tiscali's lower priority MX servers may be unresponsive or dead, contributing to delivery failures when mail transfer agents (MTAs) attempt to connect.
- Greylisting practices: Tiscali employs greylisting on its MTAs, which means initial connection attempts are often temporarily rejected, requiring senders to retry. This is a common spam prevention technique.
- Spotty response times: Beyond greylisting, Tiscali's servers are known to have inconsistent response times, which can lead to timeouts for sending mail servers that have strict connection limits.
Key considerations
- Review bounce messages: Always examine the full bounce message or Non-Delivery Report (NDR) for specific error codes, as this provides crucial context for troubleshooting. For general reasons why emails bounce, refer to this helpful guide on email bounces.
- Adjust MTA timeouts: If you manage your own mail transfer agent (MTA), consider increasing the connection timeouts to Tiscali's servers to accommodate their slower response times and greylisting practices.
- Throttle sending rates: Reduce the volume of emails sent per hour to Tiscali.it to avoid overwhelming their systems and triggering further rate-limiting or temporary rejections. This strategy is also useful for troubleshooting bounces to other major ISPs.
- Monitor blocklists: While the primary issue might be server-side, always ensure your sending IP addresses are not listed on any major public or private blacklists. Understanding how email blacklists actually work is crucial for proactive deliverability management.
What email marketers say
Email marketers often face varying experiences when sending to Tiscali.it. Some report significant bounce rates for bulk campaigns, while others see no issues with smaller, more targeted sends. The common thread is the difficulty in obtaining specific reasons for bounces from Tiscali's postmaster team, leading marketers to deduce potential causes like blacklisting or server issues.
Key opinions
- High bounce rates for bulk sends: One marketer reported over 54,000 bounces from 100,000 emails sent to Tiscali.it in a single day, even when using multiple IP addresses for their campaigns.
- Inconsistent experiences: Some marketers running campaigns into Italy do not observe general issues with Tiscali.it, suggesting the problem might be specific to sender reputation or sending patterns (e.g., bulk vs. transactional).
- Lack of transparency from ISPs: Marketers frequently express frustration over the lack of detailed information or response from Tiscali's postmaster regarding bounce reasons, making troubleshooting difficult.
- Suspected blacklisting: There's a common suspicion among marketers that high bounce rates, especially unexplained ones, could be due to an IP address or domain being placed on a blacklist or blocklist.
Key considerations
- Analyze campaign specifics: If experiencing high bounces, compare the performance of different campaigns or client sends to Tiscali.it to identify patterns or outliers. This can help you determine why a valid email address might hard bounce.
- Segment email lists: Consider segmenting your Tiscali.it recipients into smaller batches to test deliverability and potentially reduce the impact of volume-based filtering or temporary blocks.
- Review email content: Ensure your email content is not triggering spam filters. Common issues include excessive links, problematic keywords, or poor formatting. For overall deliverability improvements, read our guide on email deliverability issues.
- Sender reputation management: Maintain a strong sender reputation through consistent sending practices, list hygiene, and proper authentication (SPF, DKIM, DMARC).
Marketer view
Email marketer from Email Geeks confirms a significant number of bounces from various bulk marketing campaigns, indicating a widespread issue for high-volume senders targeting Tiscali.it.
Marketer view
Email marketer from Email Geeks notes that 54,000 out of 100,000 emails sent to Tiscali.it bounced, highlighting a severe deliverability challenge even when using multiple IPs.
What the experts say
Email deliverability experts point to specific technical issues at Tiscali.it, such as non-responsive MX servers and their implementation of greylisting, as primary causes for the Service not available bounce messages. They emphasize that senders need to adjust their mail server configurations, including timeouts and throttling, to successfully navigate Tiscali's email infrastructure.
Key opinions
- Dead backup MX server: One expert identified that Tiscali's low priority MX server (e.g., imp-5.mail.tiscali.it) was non-responsive, returning the 421 4.2.1 Service not available error upon connection attempts.
- Slow primary MX servers: Even the higher priority MX servers for Tiscali.it were noted as being slow to respond, potentially leading to timeouts for sending mail servers with aggressive timeout settings.
- Greylisting and spotty response times: Tiscali actively employs greylisting, combined with inconsistent response times from their MTAs, which complicates email delivery for senders not configured to handle these behaviors.
- Impact of MTA timeout settings: Mail servers with low timeout values are more likely to experience bounces when interacting with Tiscali's slow or temporarily unavailable servers.
Key considerations
- Increase wait times for MTAs: To counteract greylisting and slow responses, extend the waiting time for a response from Tiscali's MTAs on your sending server.
- Adjust connection timeouts: Configure your mail server's connection timeouts to be more lenient when connecting to Tiscali's infrastructure. This can also apply to other complex deliverability scenarios, such as hidden SPF DNS timeouts with Microsoft.
- Implement hourly throttling: Set up strict hourly throttling specifically for Tiscali.it recipients to reduce the volume of mail sent at once, mitigating issues caused by their system's load or rate limits. For more information about greylisting, see our detailed guide on how it works.
- Review MX records: While you can't change Tiscali's MX records, understanding their setup (e.g., priority levels) can help diagnose why certain servers are being contacted and failing.
Expert view
Expert from Email Geeks inquires about specific error messages associated with the Tiscali.it bounces, stressing the importance of detailed bounce reports for effective troubleshooting.
Expert view
Expert from Email Geeks points out that the low-priority MX server for Tiscali.it appears to be non-functional, a direct cause of Service not available errors.
What the documentation says
Technical documentation on email delivery and SMTP error codes provides a foundational understanding of bounces like 421 4.2.1 Service not available. These errors typically signify a temporary problem on the recipient's server, such as a busy server, full mailbox, or a general service interruption. Documentation often stresses the importance of understanding these temporary failures versus permanent ones, like 550 Invalid recipient.
Key findings
- Soft bounce indicators: A 4xx SMTP error code, such as 421 4.2.1 Service not available, signifies a temporary issue (soft bounce) rather than a permanent one. Senders should typically retry delivery after a delay.
- Common soft bounce causes: Documentation lists typical reasons for soft bounces, including a full recipient mailbox, a mail server being temporarily unavailable or busy, or the email size exceeding limits.
- Server-side issues: Errors like 4.2.1 usually point to a problem on the recipient's server that prevents immediate delivery, but not necessarily permanently.
Key considerations
- Retry mechanisms: Sending systems should implement appropriate retry logic with increasing delays for soft bounces, as outlined in email protocol standards. You can learn more about how different parts of the email system work together in a simple guide to DMARC, SPF, and DKIM.
- Distinguish bounce types: It's essential to differentiate between soft bounces (temporary) and hard bounces (permanent) to manage your email lists effectively. A hard bounce means the email address is invalid and should be removed.
- Analyze bounce logs: Review your mail server logs and non-delivery reports (NDRs) to pinpoint the exact error codes and messages returned by the receiving server. InMotion Hosting provides a comprehensive list of email bounce back errors and their meanings.
Technical article
Documentation from WP Mail SMTP explains that email bounces occur when messages fail to reach the recipient's inbox, likening it to a package returned due to an incorrect address.
Technical article
Mailgun's documentation details soft bounces, stating that a full recipient inbox is one of the most common reasons, implying a temporary storage issue.
Related resources
6 resources
Related pages
Why did a valid email address hard bounce, and how can I resolve it?
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A simple guide to DMARC, SPF, and DKIM
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Why your emails fail: expert guide to improve email deliverability [2025]
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