To set up an account for another person, you can certainly do so, but it is important to note that additional documentation is required by the Post Office.
To ensure that you have the necessary authorization to receive mail on someone else's behalf, you will need to fill out the postal consent forms for both yourself and the other person.
Additionally, you will need to attach a power of attorney that specifies your right to receive mail on their behalf. If you are receiving mail on behalf of an estate, you will also need to attach an executor's letter.