Every signup form makes a decision most teams never revisit after launch day: does a new subscriber land on your list the moment they type their email, or only after they confirm it. Mailchimp's study of 30,000 accounts found double opt-in lists saw 72.2% more unique opens and 114% more clicks than single opt-in lists, alongside 48.3% fewer bounces. That is not a marginal difference. It is close to a different list entirely.

What each method actually does

Single opt-in adds a subscriber to your list the instant they submit a form, no further action needed. It is the lower-friction option, and it grows a list faster. Double opt-in adds one extra step: a confirmation email the new subscriber must click before they are actually added. That extra click is doing more work than it looks like it is.

The deliverability case for double opt-in

MailMonitor's analysis of deliverability outcomes found double opt-in lists routinely exceed 97% inbox placement, compared with an average closer to 83 to 85% for single opt-in lists. The confirmation step filters out mistyped addresses, bot signups, and people who never really meant to subscribe, before any of that noise has a chance to damage your sender reputation.

It also closes off a specific abuse vector. Because single opt-in requires no confirmation, anyone can enter someone else's address, including a competitor entering addresses solely to generate spam complaints against you. Double opt-in makes that essentially impossible, since the target simply never clicks a confirmation they did not request.

IMPORTANT

A meaningful share of the industry still uses single opt-in. A 2025 Mailjet survey of US senders found roughly 40% had adopted double opt-in, 47.6% remained on single, and the rest were undecided. This is a live, ongoing trade-off, not a settled debate.

Where single opt-in still makes sense

Double opt-in is not a universal answer. It typically slows list growth by an estimated 20 to 30%, since some share of new subscribers never complete the confirmation step. For ecommerce brands and SaaS products focused on fast lead capture, where the confirmation email itself can feel like an unnecessary barrier between a genuinely interested visitor and your welcome series, single opt-in paired with disciplined list cleaning is a defensible choice.

The confirmation email is not a fixed cost

Confirmation rates are not fixed the way they are sometimes presented. With a clear subject line, a fast send, and an obvious call to action, some senders have reported confirmation rates above 90%, according to case data cited by Toptal and Scrap.io covering enterprise marketing cloud deployments. A confusing or delayed confirmation email loses far more subscribers than the extra step itself.

• Send the confirmation immediately, not hours later.
• Make the confirmation button the single, obvious action on the page, not one option among several.
• Set expectations in the confirmation subject line so it reads as the next step, not a random email.

What this means alongside your other deliverability work

Opt-in method is one input into deliverability, not the whole picture. It sits alongside authentication, covered in our SPF, DKIM, and DMARC guide, and ongoing list hygiene, covered in our guide to telling if your list needs cleaning. A double opt-in list that never gets cleaned will still decay over time. A single opt-in list paired with disciplined quarterly cleaning can close much of the gap.

Frequently asked questions

Is double opt-in legally required?

Not under CAN-SPAM in the United States, but it is treated as best practice, and required by some regional data protection frameworks. Check the specific requirements for the markets you send into.

Will double opt-in hurt my list growth?

It will slow raw signup numbers, typically by 20 to 30%, but the subscribers who complete the confirmation step tend to be considerably more engaged, which usually more than offsets the smaller list size in practice.

Can I switch from single opt-in to double opt-in later?

Yes, though the switch only applies going forward to new signups. It will not retroactively confirm your existing single opt-in list, which should be handled through list cleaning instead.

What is the single biggest risk of single opt-in?

Unconfirmed, mistyped, or maliciously entered addresses accumulating on your list undetected, quietly inflating your bounce and complaint rates on every future send.

Mail Blaze is an email marketing platform specialising in email engagement, and supports both opt-in methods with the same seven-day human support on every plan.

Run a free List Health Check to see exactly how your current list is performing, regardless of which opt-in method it was built on.

If you're weighing this decision for a brand-new list, it's worth a five-minute conversation before you build the signup form. Reach out any day of the week via our support channels or book a free demo here.