Formal legal notice
A formal legal notice puts the other side on notice of a demand or of legal action, often served through a notary or lawyer.
In removals
It asks a known publisher or person to remove content and not repeat it, and often ends the matter without litigation. Template: cease and desist letter.
Watch out
Aggressive letters can trigger the Streisand effect; have a lawyer check the text.
Frequently asked questions
Is it mandatory?
Often not, but it shows good faith and is expected before many claims.