I can but agree with David Rose and Ian Adams in their posts but perhaps there are some oddities in what they (and I, before) said.
1 Is it right that an organisation refrain from 'promoting the aims and objectives of the organisation' in its newsletter? Does not that make the editor's job in producing a newsletter of real interest to its readers far harder than it need be? Wouldn't it be good to be able to include for and against arguments for any contentious issues from their proponents?
2 Is it right that all marketing be excluded? 'Cavefest' comes to mind, an event which is independently run (and is not without critics of its management), as does the reviewing of gear (surely of interest to members, but open to accusations of marketing).
The old BCRA Newletter/Caves & Caving/Speleology included advertising, and opinion pieces, and so much of general interest that it merited a cover price for external sales. I am sure I can't be the only one to miss its complementing Descent...We have lost a lot of the expedition reports which used to come from Ghar Parau trips as a condition of funding...
I can also identify with problems in sending out material to keep members up to date with an organisation. For example, I will not be alone in being considered a life time member of a university I attended. Many years after I left, the American model of alumni funding reached the UK and marketing departments sprouted at university, departmental, and sometimes more, levels - all started sending, usually glossy, publications - increasingly with appeals to support various projects. Now, that was before PECR, but I was glad to eventually find means to opt-out, but with the option of accessing online, and archived, versions.
Whether clubs can, do, or should pass on email addresses to BCA is a whole other can of worms, but they should make it clear that CIM is full, active, voting membership of BCA and not just about insurance.
Here's a suggestion that I don't remember seeing: On BCA first being given an individual's email address, a welcome email is sent which 1) validates that address 2) asks the new addressee to sign on to the BCA Online website address to confirm their email preferences (currently for administrative and general interest categories, an explicit newsletter option could be added), which otherwise default to no electronic contact. That would cover both CIMs and DIMs, and satisfy ICO. On renewal of membership, existing preferences should carry over, but with a reminder that the option to change is always there.