On the Recipients step click the Send to box. A modal opens with a Search... field, a Most recent section (the last five groups you used, remembered in your browser) and collapsible categories: E-commerce, Lists, Ordering Systems, Pickup, Deliveries, Bag Tracking, Loyalty, Subscriptions and Lead Forms. Each entry shows its name and, where it can be calculated in advance, (N Recipients). Click the + button to add a group (a green confirmation appears and the button becomes − to remove it), and close the modal when done. Selected groups appear as tags in the Send to box; click a tag's × to remove it.

You can pick as many groups as you like; recipients are merged and duplicates (same email) are removed. Some groups need an extra value and reveal an additional field when selected: Trigger Date (for ... on X day groups), Trigger Compare Value (for People with Digital Balance <=> X) or Trigger Checkouts Count (for People who made more than X checkouts).