To send an email to all active members (with memberships) at your studio, you'll first need to create a segment to include these specific members.
Click Contacts from the top navigation bar > Segments > Create Segment.
Click Add a smart rule > Add a condition.
Click Has a Membership > select Has under "Customer Who Have / Do Not Have?" > select Any membership under "Which Memberships?" > click Save.
Add another condition > click Number of Visits > define what qualifies contacts as "active" members.
In the example below, active members have visited the studio at least 1 or more times in the past 90 days (from the current day).
If there are any qualifiers, select Specific Visits, otherwise, select All Visits under "What Types of Visits Does This Count?" and save your condition.
When scheduling your email, select your new segment for all active members under the "Recipients" drop-down.
