1. Open Rates: High open rates indicate that subscribers trust your emails enough to open them. 2. Click-Through Rates: If subscribers are clicking on links within your emails, it shows they find the content valuable and trustworthy. 3. Engagement Metrics: Look at metrics like time spent reading the email and interaction with embedded media. 4. Unsubscribe Rates: A low unsubscribe rate is a good indicator of trust, while a high rate may signal issues that need addressing. 5. Spam Complaints: Monitor the number of spam complaints to gauge if subscribers are losing trust in your emails.