custom email domains on icloud

Can anyone help.. Im trying to use a custom domain into iCloud. I can't get past the verification stage. an email for verification is sent, it's been received via my access to the webmail using my email with the correct domain. I can send /receive using the webmail, so it is working. The issue I'm having is that the verification email sent from apple has no tab to verify therefore I cannot continue the process. When I return to the iCloud custom domain page its just says verification pending.