Deliverability to GMail Customers

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50% of all of my tech support issues come from the fact that users are not getting their emails or important account notifications such as Orders, Account Activation, Shipping update, etc...100% of these are coming from GMail customers. 

Has anyone figured out a way to help against this or is there any app that lets me use my own SMTP server as I'm using Google Workspace for my email delivery. Yes I have added all of the CName stuff for my domain and email, but nothing seems to work.