This advice is a bit side-tracked.
But if GSuite doesn’t work, I recommend to use AWS SES (Simple Email Service) or SendGrid.
AWS SES is very cost effective. You can send upto 62,000 email per month for free.
It’s a bit troublesome to set-it up.
But if you are good at setting up DNS records, it should be smooth. AWS SES gives you SMTP credentials. You can set it to your Concrete easily.
You don’t need to host your Concrete on AWS server either.