The line that decides everything else.
WHAT MATTERS
Specific beats clever. Say what the message contains.
"Three things to check before the rains" beats "You won't believe this".
LENGTH
Short enough to display fully on a phone, which is where most people see it. Roughly forty characters is safe.
Anything longer is truncated mid-thought.
WHAT WORKS
A clear statement of the content A question your reader genuinely has A specific number or detail Something time-relevant, where it is true
WHAT DOES NOT
Vague curiosity with nothing behind it Excessive capitals or exclamation marks Urgency nobody believes The same phrasing every month, which stops being noticed
THE HONESTY RULE
The message must deliver what the subject promised.
A subject line that overpromises gets opened once and trains people to ignore the next.
THE SENDER NAME MATTERS MORE
Recognition produces opens more reliably than any subject line.
Consistency in the sender name is worth more than optimising the subject.
WHAT TO AVOID ENTIRELY
Re: or Fwd: on a message that is neither. It is deceptive and it damages trust permanently.
