My friend received this correspondence from a company in Spain. The words I am querying are in this phrase which is as follows.
"Con referencia al escrito enviado por usted a nuestras oficinas"
Is the term "por usted" referring to a written document sent "by" my friend, or a written document sent in his "stead", ie on his behalf.
Alternatively can the "por usted" here, be applied to both cases.