Our male cat about six months ago began pooping outside the litter box.

He's not spraying anywhere, just pooping. Like clockwork, he leaves a pile either just next to the litter box or by our door to the garage every morning or every day while we're at work. You might think it's a loneliness thing, but he's got our female cat that he plays with all day. He's also done this while we're home sitting in the next room. It's an easy clean up since it's always been on linoleum, but today we came home to poop on the mat next to the back door. I am so frustrated. He is given plenty of attention, he loves our female cat, we haven't had any major changes in the household or moving furniture or anything. I am mystified. I have heard of cats spraying, but never just pooping. Any ideas or suggestions would be appreciated!!