Hxcore.ol

Are you seeing this domain in an you're trying to troubleshoot, or Gmail assigning Message-IDs with two different domains

When you send an email, your mail client generates a to help servers track the conversation thread. Usually, this ID includes the sender's domain (e.g., @gmail.com or @outlook.com ). However, certain Microsoft applications use hxcore.ol as the domain suffix for these IDs. hxcore.ol