Is Windows Live Mail really reliable..

I had sent an email to a company on April 30, 2013 that had two attachments containing a list of the vitamins that I am on. I thought that list of Vitamins was sent although I did not hear back from the company that I had emailed, I was not overly concerned. I went to that email and found that trhe attachments with my list had been removed. That list was important to me for medical reasons. This is what I found. Prohibited file type and the attachments were considered dangerous. ???? I need that list and I was not notified . Why would any of this happen? What is dangerous about vitamins? Please help me ascertain what is going on. I am not sure that Windows Live Mail is safe after this.. I am sick about it.