Their are so many services to offer how to white list emails, I will offer a link to a page for white listing:
This does not come with a recommendation, just from a internet search to get the most basic instructions.
I would like to recommend a book by Daniel Deyette “Maximum Open Rates” A comprehensive Guide to Email Deliverability.
Just for transparency, I have read this book and use the information, I get nothing for recommending this book.
Any questions, please email me at: