Step 1: Add a Suppression Audience to LeadPost.
Navigate to Audiences and select the Email or CRM tab, and click Add Email (or CRM) Audience.
Step 2: Select the Suppression List in Your Lead Campaign.
Head to Campaigns>Lead.
Whether you're creating a new lead campaign or editing an existing campaign, you can add your suppression list under Step 4 of the Lead Campaign details.
Simply check the box next to the list you'd like to suppress, and save your changes.
For more information on CRM and Email Audiences, please visit CRM Audiences and Email Audiences.