You can send more targeted campaigns by excluding lists and segments.
An exclusion list or segment is list of contacts that you wish to exclude from your email campaign. When selecting recipients for the campaign that is ready to send you can choose a particular list or segment of recipients you don't want to receive this campaign. You can create also so called suppression list with emails that you want to keep off your campaigns forever and just select this list each time you send campaign.
Simple use case: imagine that you are collecting event registrations for a client event, some people responded on your first invitation email, but as we know often you need to send a reminder. So you can now exclude those that have already confirmed their participation in the further email reminders by adding a new list field RSVP and add Yes for each client that confirmed, then create a new segment where field value RSVP is Yes and exclude this segment. More on segments here.
To exclude list from the campaign recipients
You can exclude recipients from your email campaign in Step 2 of the Campaign Wizard.
Click on the Exclude button of the list you wish to exclude from the campaign. You can also expand a list to exclude segments created from that list.
To exclude list segments from the campaign recipients
Click on the drop down of the list segments and choose segments that you wish to exclude from the campaign.
When you click the Exclude button for any list or segment it will make sure to not send the campaign to anyone who is on an excluded list or segment.