Yes, you can.
First, you have to point your domain to Systeme IO. Refer to the article on how to point the domain name to Systeme IO.
Once you’re done pointing the domain to Systeme IO (i.e., adding a custom domain to Systeme IO), The next step is to set up the domain authentication for email within Systeme IO. The email hosting can be on your existing web hosting company.
In essence, if you have followed the steps above, you have just pointed the domain to Systeme IO so that you can use the domain for your funnels, blog, etc. You then created domain authentication (for email use purposes) to use your existing email (hosted in your existing hosting, e.g., Host ArmadaHost, BlueHost, etc.) so that you can send out emails from Systeme IO.
When someone sends you an email or reply your email, it goes to your existing mailbox (i.e., the provider who currently hosts your email)