custom email domain + own server

Hello Caneblu,

As a test, could you allow all incoming emails and see if those arrive? Here's how to do that: Allow all incoming emails to a custom email domain on iCloud.com - Apple Support

This can help narrow down some possible causes.

Let us know what happens!

Thanks for replying Caneblu,

In that case, we'd suggest following the steps at the bottom of the article that mentions:

"If you still need help

If you followed our best practices and reviewed your mail logs for more information but still can't diagnose and address delivery issues, you may contact our postmaster team by sending an email to icloudadmin@apple.com with all of the following information:

• Your company name
• Your email domain
• The IP addresses of the affected mail servers
• The SMTP errors that you're getting from iCloud mail servers
• A detailed description of the issue, including when it started

If you're not a system administrator and need help with iCloud Mail, contact Apple Support instead."

We'll place the link here for easy access: Postmaster information for iCloud Mail - Apple Support

Have a great day and thanks for using the Apple Support Communities!