Signup forms

A signup form adds the people who fill it in to your contacts. Create one in Signup forms → New form. Each form has:

• Tags added to everyone who subscribes through it, for example newsletter. Use them in segments, or start a sequence on the tag.
• Double opt-in (on by default). SendLit emails a confirmation link and subscribes the person only once they click it and press Confirm subscription. This keeps typos, fake addresses and spam traps off your list, which protects your sender reputation. The link is valid for three days.
• Redirect after signup (optional): an http(s) URL to send people to after they submit the form, and after they confirm. Without it, SendLit shows its own thank-you page.

New subscribers trigger "subscriber added" sequences, so a welcome sequence starts on its own. The confirmation email is sent through your team's email provider and appears in the transactional log.

Double opt-in needs a sending mailbox

The confirmation email has to come from somewhere, so you can't create a double opt-in form, or switch a form to double opt-in, until your team can send email. Add a mailbox under Settings → Email service providers (or ask your organization to share one), or use single opt-in.

If sending stops working later, for example because the mailbox was removed or sending was paused, the Signup forms page warns you and marks the affected forms Can't send confirmations. Until you fix it, those forms turn signups away with "This form can't accept signups right now" rather than pretending a confirmation email was sent. The API returns the reason in the form's sendingIssue field.

Share or embed a form

Every form has a hosted page at https://<your SendLit API>/f/<formId>. Open it from the form's row, or link to it from anywhere.

To put the form on your own website, choose Embed and paste the HTML. Style it as you like, but keep the field names: email (required), name (optional) and the hidden website field, which catches spam bots.

<form action="https://<your SendLit API>/f/frm_..." method="post">
  <input type="email" name="email" placeholder="you@example.com" required>
  <input type="text" name="name" placeholder="Your name">
  <input type="text" name="website" tabindex="-1" autocomplete="off"
    style="position:absolute;left:-9999px" aria-hidden="true">
  <button type="submit">Subscribe</button>
</form>

From JavaScript, post JSON to the same URL; it allows cross-origin requests:

await fetch("https://<your SendLit API>/f/frm_...", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ email, name }),
});
// 200 { "status": "confirmation_sent" | "subscribed" }
// 400 { "error": "invalid_email" }, 429 { "error": "too_many_requests" }
// 503 { "error": "form_unavailable", "message": "..." } when the team can't
//     send the confirmation email

What SendLit filters out

The answer is the same whether or not an address was accepted, so a form can't be used to find out who is on your list. (A form that can't send confirmations answers 503 to every address alike.) SendLit quietly drops:

• addresses on your suppression list, and disposable email domains (from the community-maintained disposable-email-domains list, refreshed weekly);
• submissions that fill in the hidden website field;
• more than two confirmation emails a day to one address.

Each form takes at most 10 submissions an hour from one network and 1,000 a day in total; beyond that it answers 429.

A single opt-in form subscribes new addresses straight away, but never resubscribes someone who unsubscribed. They can come back through a double opt-in form, because clicking the confirmation link proves it's them.

API and MCP

Manage forms with the /forms endpoints in the API reference or the *_signup_form MCP tools. The submission URL itself is public and needs no API key.