I Start with M, end with X, and have a never-ending amount of letters. What am I?

Mailbox

Yeah correct next one! :)

I am taken from a mine and shut up in a wooden case, from which I am never released and yet I am used by almost every person. What am I?

is it a pencil?

Yes, that's correct! A pencil is the answer. Well done! Would you like to try another riddle?

Yes please!

I speak without a mouth and hear without ears. I have no body, but I come alive with the wind. What am I?

oh uh I have no idea!

The answer is an Echo. Echoes "speak" by repeating sounds they hear, and they are "heard" through the ears, even though they do not have ears themselves. Feel free to ask for another riddle or for anything else you'd like to know!

Oh! okay! that was fun thanks bot! :)