It's well documented that Apple/iCloud has a very obscure filtering policy. Emails are delivered to the server and then disappear.
After switching our mailserver, I ran into another problem that iCloud made all my emails disappear. After playing around with my recently added header checks in Postfix, I found that iCloud expects some of those headers to be present:
/^User-Agent:/ IGNORE /^X-Mailer:/ IGNORE /^X-MimeOLE:/ IGNORE /^X-MSMail-Priority:/ IGNORE /^X-Sanitizer:/ IGNORE /^X-Originating-IP:/ IGNORE
On the other hand, removing the internal IP is OK:
/^\s*(Received: from)[^\n]*(.*)/ REPLACE $1 [127.0.0.1] (localhost [127.0.0.1])$2
Hope this helps, if you run into the same problem.