I never collect email addys from the forums. We only use the email lists collected from the projects. But the issue is as you describe.

What bothers me are the hostile reactions. Totally unnecessary as every eBlast contains a notice in the footnote on how to unsubscribe from the eBlast. And yes, I have added the how-to you suggest but it's sorta redundant at that point, as their info is already on the list. The truth is, most BOINC volunteers never make the effort to think through what that check box next to Is it OK for Project XYZ and your team (if any) to email you? implies. And IIRC that pref is an opt-out, checked by default, so it's really DA's fault.....