Because digital data (and its metadata) can be tampered with, providing reasonable proof that a document can be authenticated rests on more traditional witnesses and circumstances as well as with the IT experts (Paul Grimm has written a book on it). Leslie Wharton noted that "the threshold for establishing authenticity is very low"--a witness noting that they recall sending or receiving an email is often sufficient.  Still, you don't want to get caught out when it's crucial that you be able to make your case, so don't discount metadata as an important way to support the veracity of a file. 

Of course, you've still got to make sure no one has messed with your metadata.