If e-mail from your domain cannot be delivered to Gmail mailboxes, your domain isn't worth much. Many people, including e-shop owners etc., "solve" this by taking up a Gmail account.
But that means that you become their subject in a certain sense. Lose the account, and your livelihood is threatened.
I despise it. At this point, I don't care if my email doesn't get seen. I'll tell people to whitelist my domain if they care to see my emails. For really really urgent stuff I'll maybe use a throwaway Gmail account on the off chance.
In my experience running a small hosting provider (we had a client that sent every month a newsletter to a few tens of thousands of addresses), gmail was not the problem, fucking outlook.com and hotmail and other Microsoft domains were.
But that means that you become their subject in a certain sense. Lose the account, and your livelihood is threatened.