Custom domain email helo/hostname mismatch

I have configured an email with custom domain with the iCloud+ feature. It works good except for when I send an email to a particular domain. Then the email is undelivered. The information email mentions the following reason (the domain sent to is masked out as xyz.com)...

Final-Recipient: rfc822; ***********************************************************@*******************

Original-Recipient: rfc822;abc@xyz.com

Action: failed

Status: 5.7.1

Remote-MTA: dns; mail-server.its.xyz.com

Diagnostic-Code: smtp; 550 5.7.1

<***********************************************************@*******************>:

Recipient address rejected: Mail appeared to be SPAM or forged. Ask your

Mail/DNS-Administrator to correct HELO and DNS MX settings or to get

removed from DNSBLs; MTA helo: outbound.qs.icloud.com, MTA hostname:

p-east3-cluster6-host7-snip4-10.eps.apple.com[57.103.85.201] (helo/hostname

mismatch)

I contacted Apple support. But it was hard for me to convey that the problem lied in how apple routes the custom domain emails through temporary servers that is then flagged by the receiving server.

Any help on solving this problem will be much appreciated. Thanks.