The easiest way is: grammar/revise: your email.

Usually the more facts/points you put in in your original email, the more accurate and the more to the point.

same thing with the resume. For example, if you put "resume, software developer ", it will immediately show a generalized resume. However if you put more and more personal info and experience in, the resume will become more and more personal.

The big difference between AI and human generated letter is that, AI generated piece is quite objective, matter of fact, which is perfectly in line with office emails and resumes. However, I would prefer to write my own cover letter or personal emails by myself to add some emotional touch.

hope it helps.