What is the difference between COI and DOI?

COI (Confirmed Opt-In) and DOI (Double Opt-In) are interchangeable terms referring to the same process. They both describe a signup method where a new subscriber receives a confirmation email after submitting their information. They must click a link within this email to finalize their subscription and be added to the active mailing list. This ensures explicit consent and verifies the email address is valid and owned by the subscriber.

Does confirmed opt-in hurt list growth?

While COI/DOI helps create a cleaner, more engaged list, it can lead to slower list growth because some potential subscribers may not complete the confirmation step. This could be due to the confirmation email landing in spam, accidental deletion, or simply forgetting to click the link. However, the quality of subscribers gained through COI often outweighs the lower quantity.

Is double opt-in a legal requirement?

No, most regulations, including GDPR, do not explicitly mandate COI/DOI. However, they do require clear and explicit consent. COI/DOI is widely considered a best practice for demonstrating this explicit consent and provides strong evidence in case of a dispute, making it a highly recommended approach for compliance.

What are the alternatives if I don't use COI/DOI?

If you opt not to use COI, you should implement other robust measures. These include using real-time email validation services at the point of signup to catch invalid addresses, implementing CAPTCHAs or honeypots to deter bots, and actively monitoring your email engagement metrics. Promptly removing unengaged subscribers also helps maintain list hygiene and protect your sender reputation .

Does COI/DOI help prevent spam traps and bot sign-ups?

Yes, COI/DOI significantly helps reduce spam traps and bot sign-ups. Spambots often automate sign-ups using fake or malicious email addresses, including those that are known as spam traps. By requiring a confirmation click, you filter out these automated sign-ups, preventing your list from being polluted with bad data that could lead to being listed on an email blocklist.

Is COI/DOI email opt-in still a relevant best practice? - Compliance - Email deliverability - Knowledge base

The question of whether Confirmed Opt-In (COI) or Double Opt-In (DOI) remains a relevant best practice in email marketing is one that often sparks lively debate within the deliverability community. I've seen this discussion evolve over the years, with strong arguments on both sides.

At its core, COI (often used interchangeably with DOI) requires a new subscriber to confirm their subscription via an email, usually by clicking a link, before they are added to the active mailing list. This extra step is designed to ensure consent and reduce the chances of unwanted subscriptions.

While some argue that it introduces unnecessary friction and hampers list growth, others maintain that it's indispensable for maintaining a healthy sender reputation and achieving strong inbox placement rates. Let's delve into why this continues to be a crucial topic.

The enduring value of confirmed opt-in

Confirmed opt-in remains a cornerstone for building and maintaining a high-quality email list. By requiring a second confirmation, you significantly reduce the likelihood of invalid or mistyped email addresses entering your database. This directly translates to lower bounce rates and a cleaner list overall.

One of the most significant benefits of COI is its effectiveness in combating bot attacks and mitigating the risk of landing on an email blocklist (or blacklist) due to spam traps. Automated bots often attempt to sign up with fake or malicious email addresses, including known spam traps. COI acts as a robust gatekeeper, ensuring that only genuine, engaged subscribers make it onto your list, thereby protecting your email domain reputation.

Subscribers who complete the double opt-in process demonstrate a higher level of intent and engagement. This often leads to better open rates, click-through rates, and fewer spam complaints. These positive engagement metrics are crucial signals to Internet Service Providers (ISPs), influencing your email deliverability and inbox placement.

In addition to these technical advantages, COI provides undeniable proof of consent, which is vital for compliance with various data privacy regulations, such as GDPR. This documentation can be invaluable if you ever face questions about how a particular email address was added to your list or if a spam complaint arises. It offers a clear audit trail of explicit consent.

Balancing list growth and quality

Process pros

Accurate data: Ensures subscribers enter correct email addresses, leading to lower bounce rates and a cleaner list.
Spam trap protection: Significantly reduces the probability of bots and spam traps entering your list.
Reduced complaints: Subscribers who confirm are less likely to mark emails as spam.
Enhanced engagement: Confirmed subscribers are generally more engaged, leading to higher open and click rates.
Compliance: Provides a clear record of subscriber consent, important for regulatory adherence.

Process cons

Slower list growth: Requires an extra step, which may result in a percentage of potential subscribers not completing the process. One source suggests up to 20% won't confirm.
Lost subscribers: Some legitimate subscribers might forget to confirm, delete the email, or have it filtered to spam.
User experience: Can introduce a slight hurdle in the signup process, potentially impacting immediate gratification.
Confirmation email deliverability: The confirmation email itself needs to land in the inbox for the process to work, which depends on your overall sender health.

While COI can result in slower list growth compared to single opt-in, the quality of the list is generally superior. You're building a list of genuinely interested individuals, which pays dividends in the long run through higher engagement and lower complaint rates. The common argument that "real subscribers" are lost often doesn't hold up when dealing with opt-in forms at scale, where a significant portion of unconfirmed sign-ups are not legitimate.

Despite its advantages, some argue that COI isn't strictly necessary in all scenarios. For instance, in transactional emails or when a user explicitly creates an account or makes a purchase, the act of registration might imply consent for certain communications. However, even in these cases, an immediate welcome email or a preference center can serve a similar purpose of confirming intent without the full COI flow.

Compliance and mitigation strategies

The legal landscape also plays a role in the COI debate. While many regulations, including GDPR, emphasize explicit consent, they don't always explicitly mandate double opt-in. However, COI is widely considered a best practice by major anti-spam organizations like Spamhaus for demonstrating undeniable consent. Some countries, like Germany, have historically treated single opt-in with higher scrutiny, making COI almost a de facto requirement.

For specific industries or types of communications, the need for COI might vary. For instance, in B2B contexts where email addresses are often corporate and tied to a professional identity, the perceived risk of spam complaints might be lower than for consumer lists. However, even then, the benefits of a clean, engaged list remain.

Mitigating risks without COI

If you choose not to implement COI, it's critical to employ other robust methods to ensure list hygiene and prevent issues that can hurt your sender reputation or land you on a blocklist. While no single method is foolproof, a multi-layered approach can help. We discuss some of these alternatives in our article on mitigating risks when disabling double opt-in.

Real-time validation: Use a reputable email validation service at the point of signup to catch typos, fake email addresses, and known bots before they even reach your list.
Honeypots and CAPTCHAs: Implement these on your forms to deter automated sign-ups.
Monitoring engagement: Actively monitor your sender reputation metrics and immediately remove unengaged or suspicious subscribers.

Views from the trenches

Best practices

Always prioritize list quality over quantity by aiming for engaged subscribers.

Implement Confirmed Opt-In (COI) to verify subscriber intent and email address validity.

Regularly monitor engagement metrics to identify and re-engage inactive subscribers.

Use email validation services at signup to prevent invalid addresses and bot entries.

Maintain clear and transparent consent practices, providing an easy unsubscribe option.

Common pitfalls

Relying solely on single opt-in without additional hygiene measures can attract bots and spam traps.

Ignoring high bounce or complaint rates, which can significantly damage your sender reputation.

Failing to document consent, leading to compliance issues and difficulty proving opt-in.

Not cleaning your list of unengaged subscribers, which can signal low quality to ISPs.

Believing list cleaning services are a substitute for proper opt-in practices.

Expert tips

Ensure that your confirmation email is clear, concise, and lands in the inbox. Consider a multi-email confirmation series to maximize opt-in rates.

Don't view COI as a barrier, but as a filter that strengthens your relationship with subscribers and improves deliverability.

Even if COI isn't legally mandated, it's a strong preventative measure against spam traps and compliance challenges.

Balance strict opt-in with a smooth user experience. A well-designed confirmation flow can minimize friction.

Remember that positive engagement signals from confirmed subscribers are key to maintaining a healthy sender reputation.

Marketer view

Marketer from Email Geeks says that COI is still a highly relevant and useful best practice for all senders.

2022-05-10 - Email Geeks

Marketer view

Marketer from Email Geeks says that list bombing and bot attacks are still common, and they block a significant percentage of submissions as bots, even with advanced detection.

2022-05-10 - Email Geeks

My concluding thoughts on COI/DOI

After weighing the arguments, my stance remains that Confirmed Opt-In (COI) is indeed a highly relevant and valuable best practice for most senders. While it introduces a small amount of friction in the signup process, the benefits for email deliverability, list hygiene, and compliance often far outweigh the perceived drawbacks.

The focus should always be on building a quality list of engaged subscribers, rather than prioritizing sheer volume. A smaller, highly engaged list built with COI will almost always outperform a large, unverified list in terms of inbox placement and return on investment.

In today's stringent email ecosystem, where ISPs increasingly prioritize positive engagement and explicit consent, embracing COI helps future-proof your email program and ensures your messages reach the people who genuinely want to receive them. It's a proactive step towards long-term sending success.