Using what you know.
WHAT WORKS
Using a first name, where you collected it and it renders correctly Referring to a previous purchase Sending relevant content based on interest Acknowledging they are a customer rather than a stranger
WHAT DOES NOT
Excessive familiarity from a business they barely know Referring to browsing behaviour in a way that reveals tracking Inserting a name into every paragraph Merge fields that fail, producing "Hello ," or "Hello FIRSTNAME"
THE FAILED MERGE FIELD
The most common personalisation error, and it looks worse than no personalisation.
Set a fallback value, and test with a subscriber who has no name recorded.
WHERE THE LINE IS
Using what someone knowingly gave you is fine. Demonstrating knowledge they did not realise you had is unsettling.
THE MORE VALUABLE PERSONALISATION
Relevance. A message about something the reader actually cares about matters far more than their name at the top.
That comes from segmentation, not merge fields.
FOR A SMALL LIST
You may genuinely know your customers. Writing as though you do, without automation, works better than any personalisation feature.
