This question also has an answer here (in German):

• Schriftliche Höflichkeitsformel – Du oder du

I was taught (several decades ago) to write a capital D for all pronouns such as Du, Dir, Deine, when writing to my German penpals.

I am afraid it would look antiquated or very formal these days. Is it true? At least it seemed odd at the time.

Would you use it in chat/email exchange as well?