In the Campaign Manager in BLOX NXT Email Reach, you can choose to send to a segment or a list. Lists are groups of recipients who have opted to receive that newsletter. Segments help you to narrow lists based on combinations of engagement, lists they are on, or any personal information or custom data you have on your recipients. 

Using segments can help you to keep your lists clean and help to keep volume levels under control. It also helps to keep your KPIs in healthy rage by not sending messages to users who are no longer interested in receiving your content. 

Constant Contact: 180-day actives
Constant Contact - Re-engagement Segment