I'm not aware of any standards for "smail mail" - are there standards somewhere? I think that they would be particularly relevant. What the American Psychological Association has done is to extend their telephone standards to online work.
Email has more chance of being intercepted than paper mail, but the chance is still quite small - unless you are writing with an email account from work or school. Employers often "own" the email because they own the computer system. This apparently gives them the right to read any email they want to.
There are schools of therapy which use written work quite a bit (such as narrative therapy). Can anyone who works from this framework comment?
Leonard Holmes