Northern TV-ail Outfitters (NTO) sent a targeted email to 1,000 customers, but the actual number...

List Detective is a feature in Salesforce Marketing Cloud that scans email addresses for potential issues such as typos, invalid domains, and addresses that are known to cause bounces or spam complaints. In this case, List Detective would have identified the typo in "gmaii.com" and prevented those emails from being sent to avoid deliverability issues.

References:Salesforce Marketing Cloud Documentation on List Detective