Can I use a Proxied domain in an email client?
If your domain is proxied behind a service such as Cloudflare, you cannot use your domain as the incoming and outgoing email server in a client.
This is because the mail server you use must resolve directly to your server. Otherwise, it will cause email clients to connect to the proxy server instead of your cPanel server.
If you need to proxy your domain, it is recommended to allow the mail subdomain to resolve directly to your cPanel server so that it can be used as the incoming and outgoing server instead.