Thank-you note that isn't generic

Write a short thank-you note to {{person}}.

What they did: {{specifics}}

Name the specific thing and say what difference it made. No "I wanted to reach
out", no "truly invaluable". Three or four sentences. It should be obvious it was
written for them and not sent to forty people.

What to fill in

{{person}}

Who — e.g. a beta tester who filed six good bug reports

{{specifics}}

What they actually did — e.g. found the sync gap nobody else hit