The email is sent from Adobe's servers, by Adobe processes. This is all normal, because Adobe's site handles all the messages.
No idea about headers changing. Adobe use amazonses, like many big companies, as well as their own servers.
I'm really not sure what you are looking for or trying to prove; you will get (very sadly) fake and real messages. If you want to know if a reply is actually from Adobe staff, don't rely on Adobe in the email address, or Adobe in their name. Instead return to the forum and look in your messages. Adobe staff have an Adobe icon on their message which can't be faked. Apparently.