Is COI/DOI email opt-in still a relevant best practice?

Key findings

• Enhanced list hygiene: COI/DOI significantly improves list quality by ensuring subscribers are genuine and intentionally opted in, reducing bounce rates and the risk of acquiring spam traps.
• Reduced spam complaints: The extra confirmation step means subscribers are less likely to mark emails as spam, as they have actively confirmed their desire to receive communications.
• Improved engagement: Subscribers who complete the COI/DOI process are generally more engaged, leading to higher open and click-through rates, which positively impacts sender reputation.
• Bot and list bombing protection: COI/DOI is a strong defense against malicious bots attempting to flood lists with invalid or unwanted addresses, protecting senders from widespread email blocking and spam issues.

Key considerations

• Potential for list growth reduction: Implementing COI/DOI can lead to a lower subscriber conversion rate, as a percentage of potential subscribers may not complete the confirmation process.
• User experience impact: The additional step of confirming via email can sometimes create a fragmented or inconvenient experience for legitimate subscribers, especially in certain contexts like B2B software downloads or loyalty programs.
• Mitigating drop-off: Strategies like clear calls to action on sign-up pages and multi-email confirmation series can help encourage completion of the opt-in process.
• Legal vs. best practice: While some regulations like GDPR may imply or strongly recommend COI, it is not universally mandated, making it a strategic choice based on business needs and risk tolerance. For more on this, see our guide on whether double opt-in is required in certain countries.

Key opinions

• List quality over quantity: Many marketers prioritize a clean, engaged list, viewing COI/DOI as a crucial filter that ensures subscribers genuinely want to receive emails, even if it means slower growth.
• Protection against abuses: Marketers appreciate COI/DOI's role in preventing spam traps and list bombing, which can severely damage sender reputation and lead to email blocklists.
• Engagement benefits: The belief is strong that subscribers who take the extra step to confirm their subscription are more committed and therefore more likely to engage with content.
• Contextual application: Some marketers argue that the necessity of COI/DOI can vary by vertical or use case, suggesting it might not always be required for certain types of registrations or downloads, particularly in B2B.

Key considerations

• Conversion rate impact: A common concern is the potential for a significant drop-off in sign-ups when COI/DOI is implemented, as not all initial registrations convert into confirmed subscribers. Learn how to mitigate risks when disabling double opt-in if considering alternatives.
• User experience friction: Adding a confirmation step can introduce friction into the sign-up process, which might deter some users from completing their subscription. This is particularly relevant when considering if opt-in buttons should be checked by default.
• Alternative hygiene methods: While COI/DOI is preferred, some marketers explore alternative or supplementary methods, such as email validation services, to maintain list quality when single opt-in is used.
• Legal versus practical necessity: Marketers often weigh the legal requirements for consent against the practical benefits of COI/DOI for deliverability, especially in regions where it isn't strictly mandated. See this guide on maximizing double opt-in confirmations.

Key opinions

• COI as a fundamental best practice: Many experts strongly recommend COI/DOI for all senders, asserting its continued relevance and utility in today's email landscape.
• Protection against bots and spam traps: Experts highlight that COI/DOI is highly effective at preventing bot attacks and the accidental acquisition of spam traps, which are critical for maintaining a clean list.
• List hygiene at inception: They stress that proper list hygiene begins at the point of sign-up, and that external list cleaning services are not a substitute for robust initial opt-in processes.
• Proof of consent: COI/DOI provides irrefutable proof of a subscriber's consent, which is invaluable in addressing spam complaints and demonstrating compliance with anti-spam regulations.
• Higher engagement from confirmed subscribers: Experts observe that subscribers who complete the COI/DOI process are typically more engaged, leading to positive engagement metrics that boost sender reputation. This contributes to preventing emails from going to spam.

Key considerations

• Debate on universal necessity: While generally advocating for COI/DOI, some experts acknowledge that its necessity can be debated for certain use cases or verticals, such as loyalty programs or B2B software downloads.
• Addressing "real subscriber" drop-off: Experts argue that the majority of unconfirmed subscribers are not genuine, and that the perceived loss of "real subscribers" due to COI/DOI is often overstated.
• Beyond simple forms: They recognize that complex scenarios, like legal obligations to send to old lists, might necessitate supplementary tools like email validation services, though these are seen as complementary, not replacements for COI/DOI.
• Industry evolution: Experts reflect on how the debate around COI/DOI has evolved over time, with strong arguments remaining for its preventative benefits in a constantly changing threat landscape. A helpful resource is The Battle of the Opt-In Methods.

Key findings

• Ensures data accuracy: Documentation points out that COI/DOI ensures subscribers accurately enter their information, leading to cleaner lists and reduced bounce rates.
• Protection against malicious entries: It provides robust protection against spambot attacks and significantly reduces the probability of spam traps entering an email list, thereby improving overall list hygiene.
• Proof of consent for compliance: Documentation highlights that if spam complaints arise, COI/DOI offers concrete proof and a verifiable record of each subscriber’s opt-in confirmation, assisting with legal and compliance requirements, such as whether a two-click unsubscribe process is compliant.
• Improved sender reputation: Subscribers who confirm their opt-in are generally more engaged, contributing to higher open and click rates, which in turn boosts sender reputation and improves overall delivery and inbox placement.
• Mitigation of sign-up risks: Documentation suggests that while list growth may be more challenging, risks like accidental deletion of confirmation emails or emails being filtered to spam can be mitigated with splash pages and multi-email confirmation series.

Key considerations

• Impact on list growth targets: Documentation acknowledges that list growth can be more challenging with COI/DOI, as up to 20% of potential subscribers may not complete the email confirmation.
• Contextual application: While generally promoting COI/DOI, some guides implicitly suggest that the intensity of its necessity might depend on the specific context or legal landscape, complementing efforts like implementing DMARC.
• Beyond simple subscription: In scenarios like loyalty programs or B2B software downloads, where users provide detailed information and create accounts, the need for an additional COI step can be less emphasized in some documentation.
• Complementary practices: Documentation often recommends COI/DOI alongside other list hygiene practices, emphasizing a multi-layered approach to protecting sender reputation. This is highlighted in CampaignMonitor's guide on single versus confirmed opt-in.