Organization Administrators have the ability to upload an Opt Out/Pre-Existing "Do Not Contact" list for their Organization. First, you will need to click on the gear in the top right corner of the TextUs Web App. From that screen, you then click the "Opt Outs" tab on the left side.
You will need to create a single column spreadsheet with the header "Phone Numbers" and list all phone numbers you'd like to be added to be Opted Out from receiving messages.
Once the spreadsheet has been uploaded, all users in your Organization will be unable to text the Opted Out numbers.