What is the best way to send an opt-in email campaign such as a newsletter or database reactivation?

Use the built-in email agent instead of building a workflow. Load it with the emails you want to send and tell it to send them. It sends to the right people at the right time based on your settings.

Its features include send time optimization (sending when people are in their inbox) and sending first to the people who open and click, so inbox providers like Gmail see engagement, then sending to the rest. The agent experiments to find which emails work best.

Tell the email agent whether each email is evergreen (it could be sent tomorrow or next month) or expires (for example a sale that ends on a date). For an email that expires, set an expiration date so it is not sent after that date.