Email Subject Line Generator and Optimizer

Generate 20 email subject lines for [EMAIL PURPOSE — newsletter issue / product launch / re-engagement / cold outreach]. Email content summary: [1–2 SENTENCE SUMMARY]. Audience: [AUDIENCE]. Goal metric: [OPEN RATE / REPLY RATE / CLICK RATE]. Deliver 4 subject lines in each of these 5 categories: (1) Curiosity gap ('You're making this mistake every day'), (2) Direct benefit ('Double your open rates in 7 days'), (3) Question format ('Are you leaving 40% of your revenue on the table?'), (4) Social proof ('How [NAME/BRAND] achieved [RESULT]'), (5) Urgency or scarcity. For each subject line, add a 'Why it works' annotation of one sentence. Flag your top 3 picks and explain why.