How serious are MXToolBox blacklistings and what should I do about rented email lists?

Key findings

• Minor impact: Many blacklists shown on MXToolBox are considered low-impact or insignificant, often not used by major Internet Service Providers (ISPs) like Gmail or Outlook to filter mail.
• SORBS relevance: While most lists might be minor, a listing on SORBS could be a slight exception, acting as an early warning sign of potential problems, though its impact is often limited.
• Rented lists: Using rented or purchased email lists, even if perceived as having 'consent' through association agreements, is broadly considered unsolicited email (spam) by the deliverability community and ISPs.
• Bounce codes: Bounce codes like 550, indicating 'bad-mailbox' or 'bad-domain', are strong indicators of poor list quality and a likely consequence of sending to non-opt-in or old lists.
• Underlying issues: Blacklistings, even on minor lists, can be a symptom of fundamental problems in email acquisition or list hygiene, which could lead to more significant blockages later.

Key considerations

• Focus on impact: Instead of panicking about every blacklist, assess whether you are experiencing actual bounce increases or a drop in inbox placement. You can learn more about email blacklists and their relative importance here.
• Address root causes: Understand that blacklistings are often symptoms. The primary focus should be on improving email acquisition practices and list hygiene.
• List quality: High bounce rates, especially permanent errors (5xx), signal that your email list contains many invalid or disused addresses, which can severely harm your sender reputation.
• Long-term strategy: Relying on rented lists is not sustainable for email deliverability. It will inevitably lead to blockages and poor inbox placement over time. Consider how to manage senders and identify the cause of issues before they escalate.

Key opinions

• Inbox placement over bounces: A primary concern is whether emails are landing in the spam folder of major providers like Outlook and Gmail, rather than just seeing an uptick in hard bounces from minor blocklists.
• Company practices: Some marketers operate within company frameworks that involve using lists acquired from associations or third parties, even if they personally disagree with the practice.
• Managerial resistance: There can be significant resistance from management to change long-standing, but harmful, email list acquisition methods.
• ESP knowledge: Some managers mistakenly believe their Email Service Provider (ESP) is fully aware and implicitly approves of their list acquisition methods based on onboarding conversations.

Key considerations

• Hidden impact: While immediate bounces may not occur from minor blocklists, poor list quality from rented lists can lead to low inbox placement rates and decreased engagement, affecting overall marketing effectiveness. Learn about deliverability stats for rented email lists.
• Advocacy for change: Marketers should advocate for cleaner list practices, potentially leveraging their ESP's Terms of Service which often prohibit sending to unconsented lists. This can help address why emails go to spam.
• Long-term career perspective: Continuing to send to questionable lists can lead to severe deliverability issues that are hard to recover from, potentially impacting professional reputation.
• Proactive monitoring: Regularly checking for blacklistings and understanding their severity, even if an MXToolBox listing seems minor, can help identify emerging problems before they become critical.

Key opinions

• Low severity lists: Most blacklists shown by MXToolBox are not a major concern; many are considered to be of very low impact, used by "some dude and his cat".
• SORBS as a warning: SORBS might be a slight exception, indicating potential underlying issues that could escalate, rather than being a critical problem itself. You can find out if SORBS is an important email blocklist here.
• Unsolicited email is spam: Regardless of how lists are acquired (e.g., through association sharing), if recipients haven't directly opted in to receive mail from your specific entity, it's considered unsolicited and therefore spam.
• B2B implications: From a B2B perspective, sending to unconsented lists is seen as the "worst sort of email", leading to universal hatred and immediate blocking by recipients and filters.
• Recovery difficulty: Once a company falls into the habit of sending spam, their email program very seldom recovers, making fundamental change crucial but challenging.

Key considerations

• Prioritize major ISPs: Focus deliverability efforts on what impacts major mailbox providers (Gmail, Outlook, Yahoo) first, as they rely more on internal reputation systems than many public blocklists.
• Genuine consent: Understand that permission to share contact information among association members does not equate to permission to send marketing emails, which is a key distinction for deliverability. This relates to how your email address ends up on a blacklist.
• List hygiene: Address high bounce rates (e.g., 550 errors) by cleaning your lists. These bounces signal bad list quality and can attract spam traps, impacting your reputation. Learn more about spam traps and their effects.
• ESP policy as leverage: Use your ESP's Terms of Service as a tool to persuade management against using purchased or rented lists, as most legitimate ESPs prohibit such practices. An article from Word to the Wise provides further insight.

Key findings

• Consent is key: Official guidelines emphasize that email sending should always be permission-based, meaning recipients have actively opted in to receive communications from your specific sender identity.
• Rented lists violate policy: Documentation from major email service providers and anti-spam groups explicitly prohibits the use of rented, purchased, or scraped email lists, as they lack proper consent.
• Bounce indicators: High rates of hard bounces (e.g., 550 errors like 'mailbox not found') are documented indicators of poor list quality and are actively monitored by ISPs as a signal of problematic sending.
• Spam trap risk: Sending to non-opt-in lists significantly increases the risk of hitting spam traps, which are designed to catch senders with poor list acquisition practices and lead to severe blacklistings.
• Reputation impact: Adherence to these practices is critical for maintaining a positive sender reputation, which is the primary factor determining inbox placement across major mailbox providers.

Key considerations

• Legal compliance: Ensure all email marketing activities comply with relevant anti-spam legislation, such as CAN-SPAM in the US or GDPR in Europe, which often have stricter consent requirements than perceived third-party agreements.
• Double opt-in: Implement double opt-in for all new subscribers. This is the gold standard for proving consent and protecting against spam complaints and the associated damage to sender reputation.
• Regular list cleaning: Automate processes for identifying and removing invalid, inactive, and unengaged email addresses from your lists to prevent bounces and maintain deliverability. This practice is detailed in guides for avoiding spam traps.
• Monitor metrics: Beyond blacklist checks, consistently monitor key deliverability metrics such as open rates, click-through rates, unsubscribe rates, and spam complaint rates through your ESP or Postmaster Tools. This is part of top reasons IPs get blacklisted.