There can only be one source of truth. This is not meant in an existential way, but when you collaborate you should strive to have a central location where the stuff that matters is stored so everyone can take a look it.

If someone has a team on an issue, there should be one team-wide place where you can write it down, and more importantly where all the issues are written down. Hunting down documentation from this link in that email and this dropbox file and that sharepoint site just creates unnecessary clutter and confusion.