No override for non spam being sent to spam

Whenever I send an email from my work email to a person in my contact list (Comcast user) it goes into his spam. Every time. For years he received my emails fine but in the past 4 months I now go to spam. 

I looked at his laptop and marked each and every email as NOT SPAM.

I also set up a rule to move my emails to his inbox, but apparently rules don't apply AFTER the email is delivered, at which point I'm then in spam. So rules don't look at the spam folder? What's the point of the rules if it can't control what comes in and where it goes.  

As I researched, apparently Comcast has set up algorithms to determine if I wind up in spam multiple times, they flag me as a spammer. Not even selecting 24 emails and specifying NOT SPAM fixed it. How do I undo Comcast's algorithm that has set me as spam?

Not even having my friend send multiple emails TO me, nor having him reply to 24 emails that I had marked as NOT SPAM and were in his inbox helps.

When a user selects NOT SPAM, why won't you whitelist that email address? What's the point of having the ability to mark an email as not spam if it doesn't work?