In anger, I signed a letter to my wife saying talaaq thrice; is this divorce valid?

A letter was sent out to my wife stating that I give you talaaq thrice. 3 points I want to make: 1. I was not in a stable frame of mind, I suffer from depression. 2. It was in a moment of anger. 3. I did not personally send the letter and I had changed my mind. I signed the letter but did not post it out as I had no envelope, so I left the letter with someone who said they would get envelopes and post them out either later on or the next day. Within 24 hours, I had changed my mind, but it was too late they had already been sent out. My question is does this matter at all or does it not make a difference?