I’m not employed by CDCK, nor do I have any financial interest in pointing you to any third party services.
If you won’t want to follow the recommendation and documentation that’s your call. In this case it leads you off the path of the free support we provide here to the community, so your only other option is to engage with a consultant via the Marketplace.
This isn’t a Discourse problem, this issue is down to your mail server IP not being seen as reputable. We can’t help you fix that and you refuse to consider the options which exist for that purpose.