This question is based on this question over on Workplace SE. I am neither the OP of that question nor in any way related to the OP, I'm asking this question out of personal curiosity. In brief, the situation is that the OP has a medical issue, but his boss (verbally) threatened to fire him if he went to the doctor. Various answers in that thread are suggesting getting written proof that the boss verbally denied the trip to the doctor to use in court later.
Now, here's my question: Clearly, this boss is a jerk. Also, this boss is probably not an idiot. If he's being asked to provide in writing something that he said verbally, he's going to know something's up. Furthermore, he's probably smart enough to know that what he is doing is of questionable legal standing, so getting the boss to provide a written statement that the doctor visit was denied is easier said (written? Because webforum? Hah!) than done.
A solution to the above problem was suggested in a comment on an answer:
In the very likely case that you submit your request in writing and your boss replies verbally, write back to your boss confirming his denial. "This message confirms that on Tuesday 10am you verbally denied my urgent request for time off at X." Send a Cc to HR and Bcc yourself at a personal email address. Every time you have a "conversation" about this issue verbally, confirm back in writing.
Assume that the boss does not respond to any of these emails to confirm or deny the content as stated, and the "chain" of emails, such as it is, is completely one-sided, with the OP emailing his boss various things of this nature. My question is:
To what degree are such emails admissable in court as evidence, and what weight do they carry?
I'm tagging this question as united-states because the original question on Workplace SE was about the USA, but insight into the legal systems of other countries would also be interesting for me, just out of curiosity. I am Canadian myself, so insight into the legal system in Canada would be of particular interest (I am not in such a situation myself, I just find it interesting out of curiosity).