ISPs use various factors to calculate your sender reputation, including:
Bounce rates: High bounce rates can signal that you're sending emails to invalid addresses. Spam complaints: Frequent reports of your emails as spam can drastically lower your reputation. Engagement rates: Low open and click-through rates can indicate that your emails are not relevant or wanted. Sending volume: Sudden spikes in email volume can appear suspicious to ISPs. Blacklistings: Being listed on spam blacklists can severely damage your reputation.