feat: add customizable contact double opt-in flow (#350)
* feat: add customizable contact double opt-in flow * test: add double opt-in service coverage * fix: address review comments for double opt-in PR - Make pending status conditional on doubleOptInEnabled flag - Backfill legacy unsubscribeReason for reliable pending detection - Add doubleOptInContent to contact book listing select - Fix duplicate toast on DOI editor subject save failure - Harden searchParams parsing against string[] values - Make default DOI template use link mark for clickable URL - Make public API create+update atomic via transaction - Prevent contact upsert failure when DOI email send fails - Fix empty string template variable replacement Co-authored-by: opencode <opencode@anthropic.com> * fix: harden double opt-in confirmation safeguards Preserve explicit unsubscribe intent in DOI flows and prevent confirmation links from re-subscribing opted-out contacts. Also sanitize subscribe-page error messaging and use timing-safe hash comparison for link verification. * ui stuff * fix: require doubleOptInUrl in double opt-in templates * feat: add configurable from address for double opt-in emails * feat: add resend confirmation flow for pending contacts * fix: move subscribe confirmation to explicit POST flow * test: add contact book public API endpoint coverage * docs: add double opt-in documentation and update OpenAPI spec Add a user guide for the double opt-in feature covering setup, contact statuses, email customization, template variables, and best practices. Update the OpenAPI spec to include doubleOptIn fields in all contactBook request/response schemas. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> --------- Co-authored-by: opencode <opencode@anthropic.com> Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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KM Koushik
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---
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title: Double Opt-In
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description: "Verify new subscribers with a confirmation email before adding them to your contact book"
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---
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## Overview
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Double opt-in requires new contacts to confirm their email address before they become subscribed. When enabled on a contact book, newly added contacts receive a confirmation email with a verification link. Only after clicking the link do they become fully subscribed.
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**Why use double opt-in?**
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- Ensures email addresses are valid and owned by the subscriber
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- Reduces bounce rates and spam complaints
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- Improves deliverability and sender reputation
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- Helps comply with email marketing regulations (GDPR, CAN-SPAM)
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## How it works
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<Steps>
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<Step title="Contact is added">
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When a contact is added to a contact book with double opt-in enabled (via
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dashboard, API, or CSV import), they are created with a **Pending** status
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instead of being immediately subscribed.
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</Step>
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<Step title="Confirmation email is sent">
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A confirmation email is automatically sent to the contact with a unique
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verification link. The link is signed with HMAC-SHA256 and expires after 7
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days.
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</Step>
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<Step title="Contact confirms">
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The contact clicks the verification link in the email and confirms their
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subscription on the confirmation page.
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</Step>
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<Step title="Contact is subscribed">
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The contact's status changes from **Pending** to **Subscribed** and they
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will now receive your emails.
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</Step>
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</Steps>
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## Enabling double opt-in
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### Via the dashboard
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1. Go to [Contacts](https://app.usesend.com/contacts) and select a contact book
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2. Click on the **Double Opt-In** tab
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3. Toggle double opt-in on
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4. Customize the confirmation email (optional)
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5. Save your changes
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### Via the API
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Create a contact book with double opt-in enabled:
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```bash
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curl -X POST https://app.usesend.com/api/v1/contactBooks \
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-H "Authorization: Bearer us_your_api_key" \
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-H "Content-Type: application/json" \
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-d '{
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"name": "Newsletter Subscribers",
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"doubleOptInEnabled": true,
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"doubleOptInFrom": "Newsletter <hello@yourdomain.com>",
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"doubleOptInSubject": "Please confirm your subscription"
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}'
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```
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Or enable it on an existing contact book:
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```bash
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curl -X PATCH https://app.usesend.com/api/v1/contactBooks/{contactBookId} \
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-H "Authorization: Bearer us_your_api_key" \
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-H "Content-Type: application/json" \
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-d '{
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"doubleOptInEnabled": true
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}'
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```
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## Contact statuses
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When double opt-in is enabled, contacts have three possible statuses:
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| Status | Description |
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| ---------------- | ---------------------------------------------------------------- |
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| **Subscribed** | Contact has confirmed their subscription and will receive emails |
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| **Pending** | Contact has been added but hasn't confirmed yet |
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| **Unsubscribed** | Contact has explicitly unsubscribed |
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<Warning>
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Contacts with **Pending** status will not receive campaign emails. They will
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only receive the double opt-in confirmation email.
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</Warning>
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## Customizing the confirmation email
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You can customize three aspects of the confirmation email:
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### From address
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Set a custom sender address for confirmation emails. The address must use one of your verified domains.
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```json
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{
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"doubleOptInFrom": "Newsletter <hello@yourdomain.com>"
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}
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```
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If not set, the confirmation email will be sent from the first available verified domain.
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### Subject line
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Customize the email subject. The default is "Please confirm your subscription".
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```json
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{
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"doubleOptInSubject": "Confirm your subscription to our newsletter"
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}
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```
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### Email template
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The confirmation email body can be customized using the useSend email editor (via the dashboard) or by providing the editor JSON content via the API.
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#### Template variables
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The following variables can be used in the confirmation email template:
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| Variable | Description |
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| -------------------- | -------------------------------- |
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| `{{doubleOptInUrl}}` | The confirmation link (required) |
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| `{{email}}` | The contact's email address |
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| `{{firstName}}` | The contact's first name |
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| `{{lastName}}` | The contact's last name |
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<Warning>
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The `{{doubleOptInUrl}}` variable is **required** in the email template. The
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confirmation email cannot be saved without it. This ensures every confirmation
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email contains a working verification link.
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</Warning>
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## Resending confirmation emails
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If a contact hasn't confirmed their subscription, you can resend the confirmation email from the dashboard:
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1. Go to your contact book and find the pending contact
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2. Click the **Resend** button next to the contact
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Each resend generates a new confirmation link with a fresh 7-day expiration window.
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## Best practices
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<AccordionGroup>
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<Accordion title="Set up a verified domain first">
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Double opt-in requires at least one verified domain to send confirmation
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emails. Make sure to [verify your domain](https://app.usesend.com/domains)
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before enabling double opt-in.
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</Accordion>
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<Accordion title="Keep the confirmation email simple">
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The confirmation email should be clear and concise. Include a prominent
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confirmation button and a brief explanation of what the subscriber is
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confirming.
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</Accordion>
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<Accordion title="Use a recognizable from address">
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Use a from address that your subscribers will recognize, such as
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`newsletter@yourdomain.com` or `hello@yourdomain.com`. This reduces the
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chance of the confirmation email being marked as spam.
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</Accordion>
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<Accordion title="Monitor pending contacts">
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Regularly check for contacts stuck in Pending status. If many contacts
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aren't confirming, consider improving your confirmation email or resending
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confirmations.
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</Accordion>
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</AccordionGroup>
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