Segments
Named groups of contacts that campaigns send to.
A segment is a named audience — a group of contacts a campaign can target. Each campaign sends to exactly one segment, so segments are how you decide who receives a given send.
The list shows each segment's subscribed-member count alongside its total. Only subscribed members are mailable. A segment with zero subscribed contacts is flagged, because a campaign to it can't send.
Empty segments block sends
A campaign whose segment has no subscribed members is stopped before it sends — there's no one to mail. Watch for the "0 subscribed" / "Empty" badge in the list and fix the audience before scheduling.
Archiving & deletion
Deleting a segment archives it. Archived segments disappear from pickers, but the historical record of campaigns stays intact. You can restore an archived segment, and it's permanently swept ~30 days later once unused.
Can't archive while actively referenced
If a non-terminal campaign (draft, scheduled, sending) still targets a segment, archiving is blocked with a 409 — cancel or finish that campaign first.