Who will get my email in new flow???

We segment people to a “Win back” segment is they did not purchase from us for 180 days.  There are 3500 people on this list.

I created a new flow with a trigger based being added to this segment.  It’s not clear to me if this will also including existing people in the segment, or if it will only go to new emails added to the segment.

Here’s what I’m trying to accomplish:  send this flow to anyone already in the segment and have it automatically send as new ones enter the segment.  A bunch of emails initially transitioning to automatic emails based on segmentation.