EmailLabs tested 3 Subject Lines for the March issue of The Intevation Report (their company newsletter). A. Using Link Click-Through Tracking to Segment Your List B. 3 Tips to Improve Your Newsletter’s ROI C. Build Your List Through “Piggy-Back Marketing” And the winner was... Hint: there's a numeral in it. Their conclusion? It was simple, conveyed the benefit of opening the message and required no "translation" on the part of the recipient.