Take BES out of the picture for a moment. IBM does not even suggest running the Notes client on the same machine as a Domino server. (Yes I know the nlnotes.exe program exists when you install domino, but you are strongly cautioned to
not run it.) IBM has provided the Full Access Administration capability of the Domino Administrator client program, and you can run from your local admin PC to replace the functionality (bypassing ACLs on databases) that running the client on the PC did.
BTW, what dependency requires you ro run a mail client on a server? (this isn't a terminal server for end users, is it?). Most admin tools should have their own mailer or SMTP mailer program. And if they don't, you can always use a simple 3rd party tool like blat.exe to send emails. I can't think of a role other than a Terminal Server that would need a Notes client in a server. So what sort of a set up do you have that flies counter to this? You should really find a way to get the Notes client off of your server.
See IBM Technote # 7003449
Understanding the Full Access Administrator Feature in Domino Release 6