"mooting?"
I do not think that means what they think it means.
Filtering spam is a long solved problem and completely trivial. I receive no spam on my self hosted email, and I spend no time at all working on that.
My old unused gmail account however.... I recently logged in after more than a year. The spam folder had about 40 emails in it, and the inbox had more than 8000, all of which were spam. Google over self hosting is not a solution to spam.
You read that in Michelle Obama's voice? Weird.
....sorry. it's women's history month and all.