Hi @Promogo. Thanks for being part of GoDaddy Community! cPanel email should continue to work even if you're using our domain forwarding. However, this will only remain true as long as you continue to have a host entry on the cPanel plan. Also, you'll need to manually set up a mail.domain.com A record that points to the IP address of the cPanel plan.
Your domain probably already has a "mail" CNAME that points to @. This essentially tells the internet to look at the IP address the domain is pointed to when delivering mail. When you add forwarding, the IP address changes so it's no longer pointed to the cPanel account where the mail service is. To fix this you'll need to delete the "mail" CNAME and create a "mail" A Record that points to the IP address of the cPanel plan. This article has links and information that should help you manage your DNS records.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.