How do I litter train my adult male cat?

Hi I have a 2 and a half year old male cat. He i a purebred himalayan. He is not neutered. My problem with him i he almost never uses his litter box for going poop. He will pee in it, but he always poops in corners around my house. I've tried putting the box in these corners but he just poops next to it on the floor. I used to think it was because of territorial issues with my other cat, but she died over a year ago and this is still going on! He should be litter trained and he is an indoor only cat. Otherwise, he is a great cat. He doesn't spray or claw at things ever and he is very affectionate. This is, however, a huge problem, any tips.