Improve email reputation

I currently send out registration and other emails to new users on my website using smtp via AWS and sendmail. it would appear that only a portion of them are getting to end users and I know I don't have DKIM configured properly so I want someone to adjust all the proper configurations and show me what they did so I know for the future. The website is using Apache/Bind/PHP's mail function and I'd prefer everything communicate via smtp to AWS SES. I have attached reports from google and yahoo to provide additional information.