Workbooks Sales Leads and People records include a checkbox field called No Email.  This checkbox should contain a tick for any Leads/People who have requested not to be emailed.  You can use this field to exclude all the records that contain a tick from your report.  To do this, add a criteria to your report as shown below:

Now if you use this report to populate a mailing list, the list will exclude anyone whose record shows they've opted out of receiving emails.

Remember, the information in your report is not dynamically linked to your mailing list.  This means that if you want to re-use your mailing list in, say, 6 months time, anyone who has opted out of receiving email in the interim will still appear on your mailing list.  In this situation you can either create a new mailing list or recreate the list of recipients on your original mailing list using the original report.  (Doing this will remove all the existing recipients from your mailing list.)