Are there any objective looks at this? I know personally I manually check the spam folder, and out of the hundreds of messages a month that end up there I've ne

Are there any objective looks at this? I know personally I manually check the spam folder, and out of the hundreds of messages a month that end up there I've never seen anything important get mis-categorised. A few (<<1%) mass emails end up there inadvertently, but nothing that I would notice if I didn't check.