Spam delivery is marked by various reasons, most common one are the algorithm and filters set by ESP (Email Service Provider, like Gmail, Yahoo, etc..)
Spam delivery due to reputation of the sender domain can be fixed using DNS settings however if mails are landing in spam on corporate domains then it is impossible to identify the reason for the same as all the corporate domains have their own custom spam filters configured at their end. However, we can do a specific routing for this domain which might help in inboxing on corporate domains.