1 - Yes, although there is a very small danger of someone thinking that you "closed your mailbox with three messages", rather than "closing your mailbox by using the Close button".
Originally Posted by navi tasan
2 - Yes, the comma is OK and helps to avoid the confusion I mentioned in 1.
With both 1 and 2, I might add "still" before "unopened".
3 - No. It sounds like "He kicked me with my hands" (and that the rest of the sentence is just extra information).
4 - Yes. Having said that, I would probably not word it that way. I would have said "I had my hands tied behind my back when he kicked me" or your alternative.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.