Given that you're creating an outbound campaign, you will want to avoid both your current customers and the people that have already told you not to reach out again.
In order to address this need, Amplemarket allows you to add exclusion lists either by domain or by email, so that you never reach out to them.
You can import your do not contact list in your Ampledash under Settings --> Exclusion Lists and then you can either upload a CSV, or paste a list into the box.
By Domain or email
If you want to avoid contacting a list of domains, then the best way is to upload a CSV file with all the domains you want to exclude, with the name of the column as domain.
Your second option is to use the blue +Add emails/domains and we'll handle formatting the list.