Measuring relevance can be done through various metrics:
Open Rates A high open rate indicates that your subject lines are relevant and enticing to your audience.
Click-Through Rates A high click-through rate suggests that the content within your email resonates with your recipients and encourages them to take action.
Conversion Rates Track how many recipients are completing the desired actions, such as making a purchase or filling out a form, to gauge the effectiveness of your email content.
Unsubscribe Rates Monitoring unsubscribe rates can help you understand if your emails are missing the mark in terms of relevance.