When trying to add very similar domain names as addon domains (such as yourdomain.ie and yourdomain.com), you can get the error: (XID 7an9m5) A DNS entry for the domain yourdomain.yourdomain.ie already exists.
The reason for this is that cPanel will take the first 8 characters of the domain and try and set it as the default username/subdomain. Two subdomains cannot exist with the same spelling.
To fix this issue please see the following steps:
• Change the subdomain text field to yourdomaincom or similar when adding the second domain as an addon domain
• Leave the Document Root with the details which are auto-filled as is
• Click the blue Add Domain button which will create the addon domain
This should resolve the email issue for you, but if not, please submit a ticket and a member of our Support Dept. will be happy to advise further here.