Summary
Purchased email lists frequently exhibit high 'unknown' validation rates due to outdated, inaccurate, or scrubbed data. Validation services struggle to confirm the validity of addresses on these lists. Using them poses several problems: they damage sender reputation, violate ESP terms of service, have low engagement because of the lack of consent, can have a low ROI, and are legally problematic. Purchased lists often contain spam traps and 'graymail' addresses. Furthermore, different teams within ESPs have conflicting incentives regarding the use of purchased lists. Experts and marketers overwhelmingly recommend focusing on building organic, permission-based lists instead.
Key findings
- High Unknown Rates: Purchased lists contain outdated, inaccurate, or deliberately scrubbed data, resulting in high 'unknown' validation rates because receiving mail servers are not providing definitive answers.
- Damaged Reputation: Using purchased lists damages sender reputation, potentially leading to blacklisting and reduced deliverability, especially due to spam traps.
- ESP Violations: Sending to purchased lists violates the terms of service of many ESPs, possibly leading to account suspension, especially with ESPs like Mailchimp and Marketing Cloud having zero tolerance policies.
- Low Engagement: Recipients on purchased lists haven't opted in, resulting in low engagement rates and poor campaign performance and include 'graymail' users.
- Legal Risks: Sending to purchased lists without consent violates anti-spam laws.
- Limited Effectiveness: Cleaning or validating purchased lists doesn't guarantee improved results, as the fundamental issue is the lack of permission.
- Conflicting Incentives: ESPs may face internal conflicts between revenue generation and deliverability concerns when dealing with purchased lists.
- Bad Tool for Prospecting: Email is a bad tool for prospecting and can be bad for the ESPs' other customers as well as the sender.
Key considerations
- Focus on Permission: Prioritize building email lists through opt-in methods to ensure recipient permission and improve engagement.
- Review ESP Policies: Thoroughly review the terms of service of your ESP regarding the use of purchased lists.
- Alternative Data Acquisition: Invest in organic, permission-based list building to avoid the pitfalls associated with purchased lists.
- List Hygiene: Implement strict list hygiene practices to mitigate the impact of outdated, invalid, or unengaged addresses, potentially testing a sample of the email addresses.
- Alternative Strategies: Focus on content creation, ads and other marketing strategies to build a permission-based, highly engaged email list
- The Definition of 'Unknown': Understand what 'unknown' means when validating an email address.
What email marketers say
10 marketer opinions
Purchased email lists frequently exhibit high 'unknown' validation rates due to outdated, inaccurate, or scrubbed data. Using them poses several problems: they damage sender reputation, violate ESP terms of service, have low engagement because of the lack of consent and can have a low ROI. Purchased lists often contain spam traps, and sending to them violates anti-spam laws. Focus on building an organic list.
Key opinions
- High Unknown Rates: Purchased lists contain outdated, inaccurate, or deliberately scrubbed data, resulting in high 'unknown' validation rates.
- Damaged Reputation: Using purchased lists damages sender reputation, potentially leading to blacklisting and reduced deliverability.
- ESP Violations: Sending to purchased lists violates the terms of service of many ESPs, possibly leading to account suspension.
- Low Engagement: Recipients on purchased lists haven't opted in, resulting in low engagement rates and poor campaign performance.
- Legal Risks: Sending to purchased lists without consent violates anti-spam laws.
- Spam Traps: Purchased lists often contain spam traps that negatively affect sender reputation.
- Low ROI: Purchased lists often have a low ROI and should not be used.
Key considerations
- Data Quality: Assess data quality before purchasing any list by verifying a small sample.
- Ethical Implications: Consider the ethical implications of sending unsolicited emails.
- Alternatives: Invest in building an organic email list through opt-in methods for better results.
- Internal Alignments: Consider the different conflicting internal needs within the ESP.
Marketer view
Email marketer from Email Marketing Forum shares that high 'unknown' rates in purchased lists often indicate outdated or scrubbed data, as the provider doesn't want to guarantee deliverability on a low-quality list. They suggest verifying a small sample before purchasing a large list.
20 Apr 2023 - Email Marketing Forum
Marketer view
Email marketer from HubSpot explains that purchased lists are often filled with inactive or invalid email addresses, resulting in low open rates and click-through rates. Purchased lists can be seen as spam and can damage your brand's reputation. They also violate the terms of service of many ESPs, leading to account suspension.
19 Mar 2024 - HubSpot
What the experts say
6 expert opinions
Experts agree that purchased email lists are generally ineffective and problematic. Validation services struggle to confirm the validity of addresses on these lists, often resulting in 'unknown' statuses, and some ESPs actively ban purchased lists. Cleaning a purchased list does not make it a good list, and it's seen as a 'lazy' practice due to the lack of permission from recipients. Sending to purchased lists violates ESP policies (like Mailchimp and Marketing Cloud), which can lead to account termination.
Key opinions
- Ineffective Lists: Purchased lists are generally ineffective due to lack of recipient permission and potential for outdated information and spam traps.
- Validation Issues: Email validation services often return 'unknown' statuses for addresses on purchased lists, indicating uncertainty about their validity.
- ESP Restrictions: Many ESPs ban or discourage the use of purchased lists, with violations potentially leading to account suspension or termination.
- Cleaning Ineffective: Cleaning purchased lists does not inherently improve their quality or effectiveness.
Key considerations
- Focus on Permission: Prioritize building email lists through opt-in methods to ensure recipient permission and improve engagement.
- Review ESP Policies: Thoroughly review the terms of service of your ESP regarding the use of purchased lists.
- Legal Compliance: Consider all legal compliances and opt-in preferences when using any email marketing strategy.
- Alternative Strategies: Invest time in alternative marketing strategies such as content creation or ad campaigns.
Expert view
Expert from Email Geeks explains what "unknown" means in email validation, meaning a validator can't determine the validity of the email address. Suggests firing the customer using purchased lists.
3 Mar 2025 - Email Geeks
Expert view
Expert from Word to the Wise explains that purchased lists are not effective, because people on the list never asked to be there and will not respond well to emails. Purchased lists are often older and addresses can be full of spam traps.
7 Jul 2021 - Word to the Wise
What the documentation says
4 technical articles
Documentation suggests high 'unknown' rates in purchased email lists stem from several factors. Receiving mail servers often don't provide definitive validation answers due to greylisting, temporary unavailability, or anti-spam policies. 'Graymail' addresses (valid but unengaged) contribute to unknowns. Lists also contain spam traps and invalid addresses, damaging sender reputation and deliverability. Moreover, purchased lists often violate ESP policies.
Key findings
- Indeterminate Server Responses: Receiving mail servers intentionally avoid definitive validation responses to protect against spam.
- Graymail Addresses: 'Graymail' addresses, while technically valid, represent unengaged users and contribute to high 'unknown' rates.
- Spam Traps and Invalid Addresses: Purchased lists are prone to containing spam traps and invalid addresses, impacting sender reputation.
- Deliverability Issues: Purchased lists containing spam traps and invalids negatively affect deliverability and can lead to emails being flagged as spam.
- ESP Policy Violations: Using purchased email lists often violates the policies of most ESPs
Key considerations
- List Hygiene: Maintain stringent list hygiene practices to mitigate the impact of graymail and invalid addresses.
- Alternative Data Acquisition: Focus on organic, permission-based list building to avoid the pitfalls associated with purchased lists.
- Server Response Interpretation: Understand and interpret different server response codes to better assess email address validity.
- Email Validation: Validate email lists often to remove spam traps and invalid emails.
Technical article
Documentation from MailerCheck explains that purchased lists can be full of outdated or invalid addresses. Most ESPs don't allow sending to purchased email lists.
20 Jun 2025 - MailerCheck
Technical article
Documentation from Kickbox explains that purchased lists often contain spam traps, invalid email addresses, and recipients who never opted-in. This can significantly damage sender reputation and reduce email deliverability, as ESPs and ISPs are likely to flag emails as spam. Deliverability issues arise from purchased lists.
24 May 2023 - Kickbox
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