What is the difference between personalization in subject vs body?

Personalization itself doesn't hurt deliverability. Broken personalization does. "Hi " in the inbox screams technical failure. Missing data producing "Hi ," looks broken. Bad data producing "Hi JOHN SMITH" (from an all-caps import) looks lazy. These undermine trust and engagement.

Deceptive personalization also backfires: faking familiarity ("RE: Our conversation") or implying relationship that doesn't exist triggers suspicion and complaints. Personalization should enhance genuine relationships, not manufacture fake ones.

Personalization done right helps; done wrong, it hurts. Ensure fallbacks for missing data ("Hi there" vs "Hi "). Clean your data (proper casing, remove duplicates). Use personalization meaningfully—the recipient's name adds warmth; random data insertion adds nothing. Test personalized sends thoroughly before deployment. The goal is making recipients feel recognized, not processed by a broken mail merge.