Email marketing ROI is the net return from an email programme: (revenue − cost) ÷ cost. Revenue is the value of conversions attributed to email, while cost covers the platform, creative, and time to produce and send.
Why it matters for agencies
Email is repeatedly the highest-ROI channel because the marginal cost of one more send is near zero — the leverage is in list quality, segmentation, and deliverability rather than media spend. The honest version nets out list-building cost and uses a consistent attribution window, since email often gets last-click credit for demand created elsewhere.
Run the numbers with the free email campaign ROI calculator.