The trick to get reliably mail delivery to Yahoo back in the day was to be spending several thousand dollars a month buying ads through Yahoo.
Then when your mails to Yahoo got repeatedly blocked by Yahoo and you got tired of having to repeatedly report the false positives and and get unblocked only to get blocked again a few weeks later you have the person in charge of your ad spending call up your ad sales rep at Yahoo.
You asked the ad sales rep "Why should we keep spending $X/month on Yahoo ads to try to acquire customers, when Yahoo mail keeps blocking the receipt emails, setup instruction emails, and response emails to support questions we try to send to those customers which angers those customers and they cancel (or even try chargebacks)???".
What happened then is the sales rep puts your ad manager on hold for a few moments, then comes back with someone high up in Yahoo IT management conferenced in, and explains the situation. The high IT manager puts you all on hold, and comes back in a few minutes with someone who actually deals with maintaining the spam filters conferenced in, explains the situation, and tells the maintainer to add your domain to a special whitelist of mail that is always accepted.
Then when your mails to Yahoo got repeatedly blocked by Yahoo and you got tired of having to repeatedly report the false positives and and get unblocked only to get blocked again a few weeks later you have the person in charge of your ad spending call up your ad sales rep at Yahoo.
You asked the ad sales rep "Why should we keep spending $X/month on Yahoo ads to try to acquire customers, when Yahoo mail keeps blocking the receipt emails, setup instruction emails, and response emails to support questions we try to send to those customers which angers those customers and they cancel (or even try chargebacks)???".
What happened then is the sales rep puts your ad manager on hold for a few moments, then comes back with someone high up in Yahoo IT management conferenced in, and explains the situation. The high IT manager puts you all on hold, and comes back in a few minutes with someone who actually deals with maintaining the spam filters conferenced in, explains the situation, and tells the maintainer to add your domain to a special whitelist of mail that is always accepted.