Bounce Rates: High bounce rates can signal to ISPs that your list is not well-maintained. Spam Complaints: Frequent spam complaints can quickly degrade your reputation. Engagement Rates: Low open and click-through rates indicate that recipients are not interested in your emails. Sending Frequency: Inconsistent or overly frequent sending can raise red flags. Content Quality: Poorly designed or irrelevant content can lead to low engagement and high complaint rates.