How do we know where interaction/send message notification has come from?

Summary:

A Recruiter has received an email notification which appears to be a message from a Hiring Manager so presume they've used Send Message to the team, but the email contains no reference to requisition/candidate or Hiring Manager so how can we find out who sent it?

Content (required):

A Recruiter has received an email notification which appears to be a message from a Hiring Manager so presume they've used Send Message to the team, but the email contains no reference to requisition/candidate or Hiring Manager so how can we find out who sent it?

Version (include the version you are using, if applicable):