Code from ISP can't reach my mailbox

Hi, does anyone have this problem when a code from your ISP can't reach your mailbox on iCloud?

I'm having an issue with receiving email from some services and one of them is my ISP. I tried to set up a new account at my ISP and the reason for that was a email change. I wrote to icloudadmin@apple.com to resolve the issue but I'm not sure if that is a proper email.

I'll appreciate any support on that.

Regards