"What if I want to add 100 prospects to my campaign but I only want to reach out to 20 new prospects on a daily basis?

The solution to this is to set your Daily Prospect Start. You can set Daily Prospect Start in your campaign settings or during creating the campaign. This works by limiting the number of prospects that enters the first step. 

Watch the video to see how to set it up!

NOTE: Make sure Daily Prospect Start has been set before adding prospects to the campaign. It doesn't work if prospects were already added to the campaign then only after that you setup the prospect start. 

What I've already added the prospects and just realized that I want to update my daily prospect start? 

Answer: You would have to remove then re-add the prospects after the Daily Prospect Start is updated. Please watch the video below to see how. 

Hope that helps! You may also want to check Daily Prospect Start vs Daily Sending Limit.