Using to prima facie to imply suspicion?

Imagine that I receive a letter purportedly written by and signed off by, let's say, Sally on behalf of the company she works for (let's call the company ABC). As I read the letter I have the sense that Sally is not actually the author of the letter (instinct based on various anomalies).

Now, in my imagined reply, I open my letter as follows: Dear Sally, I refer to ABC's letter, dated 15 March 2017, which has the prima facie quality of originating from yourself; hence, my reply to you.

My question: if my intent is to imply my suspicion, but not explicitly state, that her letter was not authored by herself would I achieve this based on the wording above?

My logic is that prima facie may mean "at first appearance" and so in actuality I would be saying (the subtext, that is): on the face of it (prima facie), the received letter has your name as the author and is signed by you but we both know that you didn't really write the letter (having examined the letter in more detail).

Any and all comments will be very welcome.