Sidemail is a transactional email API platform serving SaaS developers and technical teams with focus on developer experience, template management, and analytics. The unsubscribe mechanism uses the {{{unsubscribe_url}}} merge tag placed in email templates, and Sidemail emits RFC 8058 headers automatically for authenticated sending domains. Suppression is tracked at the recipient level via API. This guide covers the tag, the developer-first API model, and how to verify the setup end to end.
Sidemail unsubscribe link
| Tag syntax | {{{unsubscribe_url}}} |
| Placement | Manual placement in transactional templates |
| Scope | Recipient-level opt-out via API |
| Config path | Dashboard > Templates > Footer configuration |
| RFC 8058 one-click | Yes, automatic for authenticated sending domains |
How to add the unsubscribe tag in Sidemail
Place the merge tag exactly as shown below in the email template. Sidemail replaces it at send time with a signed URL scoped to the recipient and campaign.
{{{unsubscribe_url}}}For custom HTML templates, wrap the tag in an anchor to render a proper hyperlink in the delivered email:
<a href="{{{unsubscribe_url}}}">Unsubscribe from this list</a>Manual placement in transactional templates
Yes, automatic for authenticated sending domains The recipient's mailbox provider (Gmail, Yahoo) uses the List-Unsubscribe-Post header to expose the native one-click button on the message. Requires domain authentication with DKIM and DMARC.
Sidemail transactional-first design means marketing broadcast is not the core use case: password resets, receipts, and lifecycle emails dominate. Transactional emails qualify for consent exemption per most jurisdictions, so unsubscribe links appear on marketing-classified templates rather than transactional. Configure the transactional vs marketing classification carefully to keep the exemption boundary clear.
Testing your Sidemail unsubscribe link
- Send a test message to a controlled Gmail address you own via the Sidemail campaign preview action
- Click the footer unsubscribe link and confirm the opt-out on the landing page
- Check the subscriber or contact record: the status should be Unsubscribed within seconds
- Verify the RFC 8058 headers in Gmail: open the message, click three dots, then Show original. Look for
List-UnsubscribeandList-Unsubscribe-Post: List-Unsubscribe=One-Click
Want the full 222-platform reference?
See the pillar guide with the compliance landscape, the RFC 8058 deep dive, and the unsubscribe tag for every ESP: How to add an unsubscribe link: the complete 2026 guide →
How to add the Sidemail unsubscribe link (step by step)
- Open your template in the Sidemail dashboard.
- Add or edit a text block in the footer.
- Insert the merge tag
{{{unsubscribe_url}}}(triple braces for HTML output). - Wrap it in an anchor:
<a href="{{{unsubscribe_url}}}">Unsubscribe</a>. - Configure the sender identity under Dashboard > Templates > Footer configuration.
- Send a test to a seed address and verify the rendered link routes to the Sidemail-hosted preference page.
Transactional-first design and marketing scoping
Sidemail transactional-first design means marketing broadcast is not the core use case: password resets, receipts, and lifecycle emails dominate. Transactional emails qualify for consent exemption per most jurisdictions, so unsubscribe links appear on marketing-classified templates rather than transactional. Configure the transactional vs marketing classification carefully to keep the exemption boundary clear. Marketing sends are tagged with unsubscribe headers; transactional sends omit them per RFC 8058 recipient-level scoping.
RFC 8058 one-click headers
Sidemail added RFC 8058 one-click unsubscribe automatically ahead of the Google and Yahoo February 2024 requirements. The List-Unsubscribe and List-Unsubscribe-Post headers inject on every marketing-classified send from domains authenticated under Dashboard > Templates. SPF and DKIM records must be verified.
Developer experience and template management
Sidemail developer-first design emphasizes template management with version history, real-time preview, and API-driven send workflows. Handlebars-style template syntax uses triple braces {{{var}}} for HTML output and double braces {{var}} for escaped strings. Recipient-level suppression via API lets applications sync unsubscribe state with customer databases in real time.
Frequently Asked Questions
What is the Sidemail unsubscribe tag?
The merge tag is {{{unsubscribe_url}}} (triple braces for HTML output). Sidemail replaces it at send time with a signed URL scoped to the recipient.
Do Sidemail transactional emails need unsubscribe links?
Not per most jurisdictions. Transactional sends (password resets, receipts) qualify for consent exemption. Marketing-classified templates include unsubscribe; transactional templates omit them.
Does Sidemail support one-click unsubscribe for Gmail and Yahoo?
Yes, automatically for authenticated domains on marketing-classified templates. Sidemail injects List-Unsubscribe and List-Unsubscribe-Post headers.
Why triple braces on the Sidemail tag?
Handlebars-style syntax: triple braces output raw HTML (needed for URL rendering), double braces escape strings for text. The unsubscribe URL uses triple braces so the anchor href is inserted correctly.
How does Sidemail compare to Courier or Postmark?
All three are transactional email APIs for developers. Sidemail emphasizes template management and analytics. Courier adds multi-channel routing. Postmark focuses on transactional deliverability. Vendor choice depends on channel scope.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
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