Double opt-in means a new subscriber has to click a confirmation link in an email before they're added to your list. Single opt-in adds them straight away, as soon as they submit your signup form.
Mailchimp puts the trade off simply: single opt-in is for fast growth, while double opt-in cuts down on spam signups and makes sure the addresses on your list are valid. That extra click costs you some subscribers who never confirm, but the people who do are real and they meant it.
Single opt-in vs double opt-in
| Single opt-in | Double opt-in | |
|---|---|---|
| Steps | Sign up and you're added | Sign up, click the link in the confirmation email, then you're added |
| List growth | Faster | Slower, because some people never confirm |
| Fake or mistyped addresses | More likely | Filtered out |
| Proof of consent | Weaker | Stronger, because the confirmation click is a record |
| In Mailchimp | The default for most audiences | The default for some EU audiences; needed for abandoned cart texts |
Mailchimp recommends double opt-in if growth isn't your main focus, or if you've had low open rates or abuse complaints. It's also required if you want to send abandoned cart text messages.
How double opt-in works in Mailchimp
Mailchimp's flow runs like this: someone fills in your signup form, passes a reCAPTCHA check, lands on a thank you page telling them to check their email, receives a confirmation email with a unique link, clicks it, and lands on a confirmation thank you page. You can add a final welcome email after that, but it's switched off by default. On Mailchimp's hosted forms, the reCAPTCHA step is required and can't be turned off.
The catch: in Mailchimp, email double opt-in only works with Mailchimp's own signup forms. It can't be switched on for form integrations or for signups coming in through the API. So if your website form feeds Mailchimp through a plugin or a connector, check how that tool handles confirmation, because Mailchimp's setting won't cover it. And if your account's primary contact address is in the EU, some of your audiences may already be set to double opt-in.
How to turn on double opt-in in Mailchimp
- Go to Audience and select the audience you want to change.
- Click the three dots and choose Audience settings.
- Open Form settings, then Email opt-in settings, and click Edit.
- Choose Double opt-in and click Save opt-in setting.
- Edit the confirmation email so it says who you are and what people signed up for.
- Test the whole flow with your own email address, and keep the confirmation records.
If you manage several audiences, Mailchimp has an Opt-In Settings page where you can change them in one go. New to the platform? My step by step Mailchimp guide walks through the basics.
Is double opt-in a legal requirement in the UK?
No, and this is where a lot of advice gets it wrong. The ICO's guidance on PECR doesn't say you need double opt-in. It says you must not send marketing emails or texts to individuals without their specific consent. Double opt-in is one good way to show you have that consent, but it isn't the rule itself.
There's one limited exception, the soft opt-in, and it only covers your own previous customers. It applies when someone bought, or negotiated to buy, a similar product or service from you, and you gave them a simple way to opt out both when you collected their details and in every message since. The ICO is clear that it doesn't cover prospective customers, new contacts or bought in lists, and it doesn't cover charity fundraising or political campaigning.
A few more points from the ICO that small businesses often don't know:
- Sole traders and some partnerships count as individuals, so the consent rules apply to them.
- You can email corporate bodies such as companies, Scottish partnerships, LLPs and government bodies, though keeping a list of anyone who's objected is good practice.
- You must not hide who you are, and you must give a valid address people can use to opt out.
- Every email needs an opt out, by reply or unsubscribe link, and you need to act on it promptly and keep a list of people who've opted out.
- Asking people to forward your marketing or hand over their friends' details still has to follow PECR, and the ICO advises against collecting friends' details.
Outside the UK, Mailchimp's point is that consent rules vary by country, but they all come back to one thing: you need permission from anyone you send marketing email to. The US CAN-SPAM Act and Canada's anti spam law, CASL are two examples Mailchimp names.
The soft opt-in in practice
Say you sold someone a course last year, and you gave them an easy way to opt out at checkout and in every email since. Under the soft opt-in, you can email them about a similar course.
Now say you buy a list of local business owners, and most of them are sole traders. That's a bought in list, so the soft opt-in doesn't apply, and because sole traders count as individuals, you'd need each person's specific consent before you email them. That's exactly the situation where a double opt-in signup earns its keep, because the confirmation click shows they said yes.
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One Mailchimp point if your account is EU based: some audiences may already default to double opt-in, but you can change each audience to single opt-in if you'd rather, from the same Email opt-in settings screen.
If you manage your own inbox, check turning off Gmail smart features.
My verdict
For a small list, I'd use double opt-in. Yes, you'll grow a bit more slowly, but you'll get fewer fake and mistyped addresses, a cleaner list, and a click that shows each person said yes. Just don't let anyone tell you UK law demands it. What the ICO wants is specific consent you can show, an easy way out in every email, and a suppression list you keep up to date.
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Frequently asked questions
What is the difference between single and double opt-in?
Single opt-in adds subscribers as soon as they submit your form. Double opt-in sends them a confirmation email first, and they're only added once they click the link.
Does UK law require double opt-in?
No. The ICO's PECR guidance requires specific consent for marketing emails to individuals, with a soft opt-in exception for previous customers. Double opt-in is one way to evidence consent, not a legal requirement.
Can I use double opt-in with Mailchimp's API?
No. Mailchimp says email double opt-in can only be enabled for Mailchimp signup forms, not for form integrations or the API.
Does the soft opt-in cover new leads?
No. The ICO says the soft opt-in doesn't apply to prospective customers, new contacts or bought in lists.
Is Mailchimp's welcome email sent automatically after double opt-in?
Not by default. Mailchimp's final welcome email is optional and disabled unless you turn it on.
