If you are a recipient and notice this string in your "Show Original" or "View Headers" option, it generally means:
: Using a dedicated domain like hxcore.ol helps infrastructure providers monitor delivery rates and manage bounce-backs without cluttering the client's primary domain reputation. Why Do I See This in My Email? hxcore.ol
A standard Message-ID looks like unique-string@domain.com . In cases involving hxcore.ol, you might see a format such as *@hxcore.ol . If you are a recipient and notice this
Understanding hxcore.ol: A Technical Deep Dive into Email Message IDs hxcore.ol