Email notifications setup that is robust and don't end up in recipients junk mail

Question

I have been setting up a few email integrations over the years and I have used mailgun, sendgrid and lately Amazon SES.

I still have not experienced a setup that works silky buttery smooth and ends up in the right location (not junk mail) 100% of the time. We recently changed from Sendgrid to Amazon SES which improved the sending reliability, however, it seems like for some users, specifically outlook users some emails end up in junk whereas some don't. To be clear this happens for the same user. We do not use the domain for marketing emails or such, only notifications such as "forgot password" or updates of events in the system.

We think we do take all the steps necessary on SES such as validating our mailbox with verified identities (https://docs.aws.amazon.com/ses/latest/dg/verify-addresses-and-domains.html)

The questions

1. I would like to get a solid understanding for what is needed to setup a good email notification system that works 100% of the time. Is that even possible. Is there a good reference for the fundamentals that is service agnostic?

2. What is the best way to do this on AWS SES

Not acceptable answers

1. Answers such as "Use text messaging or in app notifications".
2. Answers that recommend other services without explaning what the specific problem is and why it happens.