Summary
NetZero and Juno, now operating under United Online, primarily utilize their own proprietary (homegrown) spam filters, which can pose unique challenges for email deliverability professionals. Unlike larger email providers that might use widely recognized third-party blocklists and filtering solutions, these older, smaller ISPs often have less transparent systems. Senders, particularly during IP warming, may experience unexpected blocking even with highly engaged audiences and otherwise good deliverability to other providers. The key to resolving these issues lies in understanding their specific postmaster guidelines and diligently managing sender reputation.
Key findings
- Homegrown filters: NetZero and Juno (now part of United Online) primarily use their own proprietary spam filtering systems, which can be less predictable than commercial solutions.
- IP warming challenges: Senders may encounter blocking during the early stages of IP warming, even when targeting highly engaged subscribers and experiencing good deliverability elsewhere.
- Postmaster contact: United Online provides a specific postmaster page for resolving blocking issues, which has been reported to be responsive.
- Consolidation issues: The complex ownership structures of smaller ISPs (e.g., Earthlink being under Windstream Holdings) make it difficult to track their current affiliations and mitigation processes.
- Old but not tiny: Despite their age, NetZero and Juno are not insignificant, maintaining a user base that requires careful deliverability management.
Key considerations
- Direct engagement: For specific blocks, especially during IP warming, direct communication with the ISP's postmaster team via their designated channels is crucial.
- Maintain reputation: Ensure your IP and domain maintain a pristine sender reputation, as these ISPs may have lower thresholds for blocking. Understanding your domain reputation is key.
- Monitor bounce codes: Pay close attention to specific bounce codes received from NetZero and Juno. For instance, a 5.3.2 soft bounce error indicates specific issues that need addressing.
- Content and infrastructure: Even with good IP reputation, content or specific infrastructure configurations can trigger filters. Regularly check for potential spam filter triggers.
- Centralized resources: Keep an updated list of postmaster contacts for all ISPs, especially smaller ones, as this information is often disparate.
What email marketers say
Email marketers frequently express frustration with the opaque nature of spam filters employed by smaller or legacy internet service providers like NetZero and Juno. These platforms often present unique deliverability challenges that differ from those encountered with major providers. The general consensus highlights the difficulty in identifying specific blocking mechanisms and the ongoing need for a centralized resource to manage postmaster contacts and mitigation strategies.
Key opinions
- Frustration with smaller ISPs: Marketers find it challenging to keep up with the changing ownership and specific mitigation requirements of numerous smaller ISPs.
- Need for centralized lists: There's a strong desire for a comprehensive, centralized database of ISP postmaster contacts to streamline troubleshooting and delisting processes.
- Unpredictable blocking: Even with best practices like sending to engaged subscribers and minimal bounces, blocks can occur with these older services during critical phases like IP warming.
- Legacy challenges: NetZero and Juno are viewed as older, established services rather than simply tiny ones, implying a different set of historical or ingrained filtering behaviors.
Key considerations
- Persistent effort: Resolving blocks with NetZero and Juno may require persistent investigation and outreach due to their unique (and potentially less documented) filtering logic. This is similar to challenges seen with small ISPs.
- Resource sharing: Marketers often rely on shared community knowledge and master files of postmaster contacts to navigate these niche blocking issues.
- IP reputation management: Even with successful IP warming to major providers, specific attention is needed for older ISPs that might have more sensitive internal reputation systems or utilize different blocklists.
- Port blocking: Awareness that some ISPs, including Juno and NetZero, might block outgoing SMTP Port 25 is important, as this affects how mail is sent from their networks.
Marketer view
Marketer from Email Geeks notes the constant challenge of trying to track which parent companies own smaller ISPs and understanding their specific mitigation processes. It's a never-ending task to keep up.
Marketer view
Marketer from Email Marketing Forum describes encountering blocks on NetZero and Juno during IP warming, despite targeting highly engaged subscribers and seeing good performance elsewhere. It's a frustrating bottleneck.
What the experts say
Industry experts concur that NetZero and Juno (under United Online) predominantly rely on proprietary, homegrown spam filtering systems. This characteristic often leads to less transparent blocking behavior compared to ISPs using widely adopted solutions. Experts emphasize the importance of traditional deliverability best practices, combined with direct, tailored outreach to these providers' postmaster teams when encountering blocks, particularly during IP warming or reputation building.
Key opinions
- Homegrown filter prevalence: Many older ISPs, including NetZero and Juno, developed their own spam filters rather than relying on external services.
- Limited transparency: These proprietary systems can be opaque, making it difficult for senders to diagnose specific block reasons or predict filtering actions.
- Sender reputation sensitivity: Older ISPs may have lower tolerance for even minor reputation issues, leading to quicker blocklist (or blacklist) placements.
- Importance of postmaster contact: Direct communication via postmaster forms or specified channels is often the most effective route for delisting and resolving persistent issues.
- Challenges with consolidation: Corporate mergers and acquisitions can alter filtering policies and contact points, requiring ongoing research by deliverability teams.
Key considerations
- Dedicated warming for legacy ISPs: Implement a more conservative IP warming strategy specifically for these sensitive domains, even if other providers are accepting mail smoothly.
- Monitor unique blocklists: While common DNSBLs (DNS-based blocklists) are important, be aware that NetZero and Juno might use internal, less public blocklists or blacklists.
- Content review: Ensure your email content adheres to strict best practices, as these filters may be more aggressive in flagging suspicious keywords, formatting, or sending patterns.
- Verify authentication: Double-check your SPF, DKIM, and DMARC records for proper configuration, as authentication failures can lead to immediate blocking by any ISP, regardless of their filter type. You can learn more about DMARC, SPF, and DKIM in our guides.
Expert view
Expert from Spamresource.com indicates that older ISPs like NetZero and Juno often rely on internally developed spam filters rather than common third-party solutions, making their behavior unique.
Expert view
Expert from Wordtothewise.com explains that these homegrown filtering systems can be less transparent and more reactive to sender behavior, making them particularly challenging to troubleshoot without direct insight.
What the documentation says
Official documentation and technical resources indicate that older ISPs such as NetZero and Juno (under United Online) have specific, often internally managed, policies and procedures for handling incoming email and resolving blocking issues. These documents emphasize general best practices for senders, including adherence to established protocols, careful content creation, and proper authentication. While they may not detail the exact algorithms of their spam filters, they provide clear channels for senders to request delisting or inquire about delivery problems.
Key findings
- Specific Postmaster sites: United Online (which includes Juno and NetZero) provides a dedicated postmaster site for handling blocked senders and inquiries.
- General spam filter triggers: Documentation often outlines common factors that trigger spam filters, such as problematic content, poor sender reputation, or misconfigured DNS records.
- Port blocking: Some ISPs, including Juno and NetZero, are reported to block outgoing SMTP Port 25, which can impact email transmission.
- FCrDNS importance: Forward Confirmed reverse DNS (FCrDNS) is a significant factor many spam filters use to determine the trustworthiness of an email source. Failing this check increases the likelihood of blocking.
Key considerations
- Adherence to policies: Always consult the specific postmaster pages for each ISP to understand their unique requirements and procedures for delisting or troubleshooting.
- Comprehensive spam checks: Utilize spam checking tools to identify potential content or technical issues that might trigger filters, even those that are homegrown.
- Authentication configuration: Ensure all email authentication standards like SPF, DKIM, and DMARC are correctly implemented, as these are fundamental to proving sender legitimacy to any filter.
- Network-level issues: Investigate potential network-level blocks, such as port blocking, that could prevent your emails from even reaching the spam filter itself.
Technical article
Documentation from postmaster.untd.com states that United Online, the parent company of Juno and NetZero, maintains specific policies and procedures to prevent spam and ensure the delivery of legitimate email, directing senders to their blocked senders form for assistance.
Technical article
Documentation from DuoCircle mentions that regularly running a spam check can help narrow down the various reasons why genuine emails might be blocked as spam, outlining a checklist of common triggers.
Related resources
5 resources
Related pages
What does a 5.3.2 soft bounce error code mean when sending emails to Juno and NetZero?
How to resolve 'Blacklisted by Internal Reputation Service' email bounces from small ISPs?
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Why your emails are going to spam in 2024 and how to fix it
What is an email blacklist and how does it work?
Boost email deliverability rates: technical solutions from top performing senders
A simple guide to DMARC, SPF, and DKIM
What filtering methods do Optimum, Windstream, and CenturyLink use for email, and how can I troubleshoot content-related blocks?
What happens when your domain is on an email blacklist?
How your email address ends up on a blacklist
