Your bot tags leads that do not want to be contacted again. This includes leads that explicitly say they do not want to be contacted again or that ask to be removed from your mailing list.
You can see who these people are by exporting your leads. or filtering leads based on lead owner via the Lead Attribute "Do Not Contact."
The leads will appear in a column called "Tags." You will see the tag
'Do Not Contact' in this column if a lead has asked to not receive emails from you in the future.
Filtering leads based on lead owner when re-engaging will help ensure that your bot does not attempt re-engagement with leads that no longer what to be contacted (e.g. leads who requested to unsubscribe).