What is the "Sub" (SubscribeLink) button in the message editor for?

The "Sub" (SubscribeLink) button in the message editor is to be used only when designing a customer "Subscription Confirmation Request" message.

That's the message that you can configure the system to send to pending subscribers to request that they confirm their intent to subscribe to your messages (double opt-in or confirmed opt-in approach, which is the recommended way to handle the subscription process).

To activate a subscription confirmation link in a message:

1. load the message in the message editor
2. enter text or an image in the message (E.g. "Confirm your subscription" text link)
3. select it
4. click the "Sub" icon to turn it into a link to confirming the subscription