I received a job offer on relative short term notice. Everything was settled by phone, but obviously I had to sign a contract and send it back to the company.
Instead of writing and printing a full cover letter, I simply stuck a small note (post-it) on top of the document-folder, saying something like 'Dear Mrs. X, as discussed on phone I'll hand in document Y later. Thanks, ...'.
Was this rude? When is it appropriate to use post-its instead of cover letters?
If it matters: country was Germany, the company quite large, the communication was with my future contact person in HR. We had contact via mail and phone about the contracting process beforehand.