I don't like to give advice but...
If it was me I think I would take the letter home without reading in and burn it or run it through a shredder. I think I would get some sort of emotional release from whatever bonds that held me by doing this. The strength to get the letter, the courage to not read it and then destroying it because it's not something I need for my recovery. My recovery comes from within, not from the letter's of alcoholic ex's.
Your friend,