To demonstrate the effectiveness of an email marketing campaign in generating new sales leads, the most relevant metric to present to the head of sales is conversions. Conversions refer to the actions that email recipients take as a direct result of the campaign that align with predefined goals, such as filling out a contact form, signing up for a webinar, or making a purchase. This metric directly correlates email engagement with the desired outcome of acquiring new sales leads, providing a tangible measure of the campaign's impact on business objectives.

Focusing on conversions allows the marketing team to quantify the effectiveness of the email campaign in driving meaningful actions that contribute to the sales pipeline.