Mechanic doesn't permit bulk email messages, in which the same content is sent to many customers at once. As a rule of thumb: if an email requires an unsubscribe link, it shouldn't be sent using Mechanic. (Learn more about this.)
In the rare case that an email does warrant an unsubscribe link, use {{ customer.unsubscribe_url }} to add a link, like this:
<a href="{{ customer.unsubscribe_url }}">Unsubscribe</a>
This property of the customer object points to a Mechanic-powered URL that...
- Turns off the "Accepts marketing" property of the related customer, in their Shopify records
- Gives the customer a link to return them to the Shopify store's online storefront
{% hint style="info" %}
If your task code doesn't have a customer object, you might have to write some different Liquid code to achieve the same ends. The idea is to call the unsubscribe_url attribute of the appropriate customer object, regardless of what specific variable holds the customer object.
{% endhint %}