Rule reminder
Formal register adapts to context: business letters use 'Egregio/Gentile', academic texts use impersonal and passive, legal documents use 'ai sensi di' and nominalisations, HR communications use 'si comunica che' and 'è tenuto a'. The key is consistency — every element of the text must match the chosen register.
You are writing a formal complaint to a company whose service failed. Which opening is correct?