More and more people are reporting this weird "too many hops" error when sending email to their custom domain.
The consensus is that it only affects older iCloud users who joined the service during either iTools, .Mac or MobileMe days. In other words, if your iCloud email address has either @mac.com or @me.com alias (in addition to @icloud.com), you are affected. If your iCloud email address only has @icloud.com ending, you are not affected.
Only Apple can fix this. There's nothing you can do, except report it.
The consensus is that it only affects older iCloud users who joined the service during either iTools, .Mac or MobileMe days. In other words, if your iCloud email address has either @mac.com or @me.com alias (in addition to @icloud.com), you are affected. If your iCloud email address only has @icloud.com ending, you are not affected.
Only Apple can fix this. There's nothing you can do, except report it.