I've had the same thing happen.

From the other side, when I've listed things on CL some replies I get seem legit but set off my email's "danger!" warning so I don't touch them (unless there's a phone number, then I'd call). I've thought that maybe the same thing is happening to emails I send, so they're getting ignored.

I don't know, but if that's the case I would think the fact that you include your number would set people at ease, but apparently not.