This feature was originally available on free plans, but we had to limit it to paid plans two years ago. Unfortunately, it was being exploited by individuals for fraudulent activities, where they created free accounts and used the Autoresponder to send spam emails.
To protect against this misuse, we had to make the decision to restrict it to paid plans.
I hope this clears things up!
If you have any further questions, feel free to ask. We’re always happy to help