Domain already uses Gmail as email service

Domain already uses Gmail as email service

Hello,

My business is a franchise and I don't have direct access to the domain.

The company uses Gmail and I have my address IMAP'ed to sales inbox now, but I am told if I send an email from salesinbox its likely to go to spam VS sending from gmail directly.

By sending directly from Gmail i'm loosing all the sales signals and analytics for open rates.

Is there a way to authenticate the domain for my 2 email addresses without the entire franchise having to get off gmail?

Thanks