Purchased email lists frequently exhibit high 'unknown' validation rates due to outdated, inaccurate, or scrubbed data.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.
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Purchased email lists frequently exhibit high 'unknown' validation rates due to outdated, inaccurate, or scrubbed data.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.
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Email marketer from Email Marketing Forum shares that high 'unknown' rates in purchased lists often indicate outdated or scrubbed data, as the provider doesn't want to guarantee deliverability on a low-quality list.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.
5 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.
3 Mar 2024 - HubSpot
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.
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.
16 Feb 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.
22 Jun 2021 - Word to the Wise
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.
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.
4 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.
9 May 2023 - Kickbox
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