This is always a difficult question, but the answer goes back to the three reasons why we believe companies should...
look into email archiving in the first place. If you're subject to records retention regulations, two supporters of a project should definitely be a records manager as well as a compliance officer. These two groups tend to have budgets, and they definitely have to look at electronic records management programs as they pertain to email. So in my opinion, that's the first place to go, especially if you're regulated to get some sponsorship.
So, storage managers as well as some key employees could be essentially the third group that supports any type of email archiving project. It's key to remember that it's not mutually exclusive for each of those groups to have to go do their own thing. You can get the benefits of compliance, e-discovery mailbox management with one solution typically, so having one or more of those groups support an effort or support a project would certainly increase the likelihood that it gets approved, or at least gets funded.
Go back to the beginning of the Email Archiving in 2008 FAQ Guide.