Hi there,

Thanks for posting your question to the Community and hope I can help!

So the first step to sending a campaign to new people in a segment would be first to isolate the people who have already received your campaign. Let’s call the campaign just “X”. In order to capture those people who you have already sent campaign X to in your segment, we will need to make a new definition.

The following conditions would be that if that person has done → received email → 1 time → over all time; where subject = X (name of your campaign email). (please see screenshot attached for visual)

After creating this segment and cloning the campaign, we are going to refer to this article on “How to Exclude Lists or Segments from a Campaign”. We are going to follow the steps outlined in the article:

1. We are going to include everyone from the original segment you have created as the recipients of this campaign. 
2. Select the new segment we made from the previous paragraph of “people who have received email 1 time over all time with the subject being X” to be excluded

The result when you send the campaign is it will only target net-new people who have joined the segment since the initial campaign send!

Hope this was helpful and please let me know if there are further questions!

Have a good day,

Alex