so you mean you want to use business email for free?no i want to use a business email ...@... .com to send emails to customer but a bueiness email in google is paid now, i search how to receive client emails in WHMCS and send email from WHMCS to client gmail using sendinblue for example or mailgun.
i don't think there is anything like it, you have to pay for it, at least to rent hosting that can be used to send emails, look for one that uses the cpanel / directadmin control panel to make it easier.