The decision in one paragraph
Single opt-in adds a subscriber the moment they submit a form. Double opt-in (confirmed opt-in) sends a confirmation email first and adds them only after they click. Single opt-in grows a list faster; double opt-in keeps typos, bots and people who will never read out of it. For small businesses whose deliverability depends on a few hundred engaged readers, the cleaner list usually matters more than the extra signups.
What Kit and MailerLite document
| Question | Kit | MailerLite |
|---|---|---|
| Default on new forms | Double opt-in is the default setting [1] | Double opt-in is enabled by default when you create a form [3] |
| How to keep it on | Keep Send confirmation email checked and Auto-confirm new subscribers unchecked [1] | Toggle on the form Overview page [3] |
| Editing the confirmation email | Edited under the Confirmation Email tab in form settings [5] | Only on paid plans [3] |
| API and integration signups | Not covered in the cited articles; check your integration | Separate setting: Double opt-in for API and integrations, under Subscribe settings [3] |
| Imported contacts | Automatically confirmed on the form, even with double opt-in [2] | Imported Unconfirmed contacts stay non-sendable (see migration guide) |
| If Send confirmation email is unchecked | Disabling the confirmation email also disables double opt-in [5] | Not applicable |
When double opt-in is the better choice
- Public forms on your website, especially with a free download, which attract typos and fake addresses.
- Any list you plan to grow past a few hundred, where spam complaints and bounces start to affect delivery.
- Audiences in places where you may need to show evidence of consent. Confirmation gives you a timestamped record.
- A free download: sending it by email after confirmation also proves the address works.
When single opt-in can be reasonable
- Customers who opted in at checkout where the purchase itself confirms the address.
- In-person signups at an event where you record the consent and the source.
- An internal or client list where every address is known and verified.
- In all three cases, record when and how consent was given, because you will not have a confirmation click as evidence.
Write the confirmation step so people finish it
Most of the cost of double opt-in is people who never click the confirmation link. You can recover much of that with wording, and you need no extra tools.
- Thank-you page: say there is one more step, name the sender and the subject line to look for, and mention spam and promotions folders.
- Confirmation email subject: say what it is, for example "Confirm your subscription to <newsletter name>", instead of a clever teaser.
- Body: put one prominent button near the top and keep the text short.
- Sender: use a recognizable name and an address on your own authenticated domain.
- Test: sign up yourself with a Gmail address and an Outlook address before you publish the form.
Pitfalls that cost signups
- Confirmation email from an unverified or unauthenticated sender lands in spam. Authenticate your domain first.
- Form thank-you page says "You are subscribed!" rather than "Check your inbox to confirm."
- Welcome automation triggers on form submit in a way that conflicts with confirmation. In MailerLite with several forms, only the automation tied to the form where the person confirms will trigger; use a group trigger for multi-form setups (see our welcome-email guide).
- Expecting to chase unconfirmed people later. MailerLite does not allow resending the confirmation email. [4]
- Turning off Send confirmation email in Kit to fix a delivery problem. Kit warns that disabling it also disables double opt-in. [5]
Our rule
Keep the default double opt-in on public forms. Rewrite the thank-you page and the confirmation email subject so people understand there is one more step. Use single opt-in only for sources where consent is verified another way, and keep a short written note of that source for each list.
Questions before you decide
Can I resend the confirmation email to unconfirmed subscribers?
MailerLite says it is not allowed to resend double opt-in emails to unconfirmed subscribers, though a person who signs up again through a double opt-in form receives another confirmation. Plan your form copy so people know to check their inbox.
Do imported subscribers get a confirmation email in Kit?
No. Kit says subscribers imported into a form are automatically confirmed on that form, even with double opt-in enabled, which is why you need permission before importing.
Can unconfirmed subscribers receive my newsletter?
Not in MailerLite: its help center says unconfirmed subscribers cannot receive newsletters and only active subscribers can.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- Kit Help: The all-important double opt-in Accessed 13 Oct 2026
- Kit Help: Importing subscribers into Kit, what to know and FAQs Accessed 13 Oct 2026
- MailerLite Help: How to use double opt-in when collecting subscribers Accessed 13 Oct 2026
- MailerLite Help: What are unconfirmed subscribers? Accessed 13 Oct 2026
- Kit Help: The confirmation email Accessed 13 Oct 2026
Sources link directly to providers. Product buttons may use separately labeled affiliate links. Read our disclosure.