I wouldn't post any names publicly here for fear of scamming. Believe me. I just had to clean up a whole big mess on my personal email account because of settings in WHM. A feature was turned off by default, which WHM recommend you turn on, to stop spam. Probably up to 20k emails a day. It was a nightmare to get under control. Which it thankfully is. Except for my reputation, that is
Two different Hosts seemed helpless. Not a clue what to do. You ask them, looking for help. But they are at least as helpless as you are, yourself
You really have to dig DEEP into WHM to find the answers yourself. By trial and error. Not the best of scenarios.