A marketing associate at Northern Trail Outfitters (NTO) notices the number of hard bounces increased...

The increase in hard bounces experienced by Northern Trail Outfitters (NTO) after incorporating a new list of contacts from an industry event is most likely due to some of the newly added contacts having invalid email addresses. Hard bounces typically occur when an email address is incorrect, nonexistent, or has been deactivated. When a list is newly integrated into a sendable data extension without thorough validation or cleaning, there's a higher likelihood that it contains email addresses that are no longer valid, leading to an increase in hard bounces.

It's essential for marketing teams to perform email address validation and list cleaning, especially when incorporating new lists from external sources like industry events, to maintain email deliverability and sender reputation.