Delivery is not dependent on authentication

What really drives delivery, particularly at the consumer mailbox providers, is engagement.

The big drivers of engagement are

  1. having permission to send email and
  2. sending mail users want to receive and interact with.

Authentication is there so that the filtering engines know what mail is actually from you. It allows them to be really harsh on spam forging your domain or sent without your authority and still delivering your legitimate mail to the inbox. If your mail is fully authenticated and still going to the bulk folder, then the problem is related to your email. Something you’re doing, whether it’s a permission problem or an engagement problem or whatever, is making the filters think your mail isn’t wanted.

Fixing authentication isn’t going to fix delivery problems caused by authenticated email.