Case Flag Functionality and Internal User Emails
There is an option in the Case Flags Setup Wizard that specifies that a case flag will be set if the email domain does not equal the company domain specified in the Optional Setup section of the Case Flags Setup Wizard. This means that if an internal user with the same company domain responds to the case email, a case flag will not be set.
Example: A company domain of ic.com is set in the Company Domain field in the Optional Setup section of the Case Flags Setup Wizard. Jane (firstname.lastname@example.org) sends a message regarding case 001. Bob (email@example.com) responds to the case email, but no flag is set on the case.
The solution for this scenario is to clear the Company Domain field under Optional Setup in the Case Flags Setup Wizard. If there is no Company Domain supplied, internal users will be able to set the Case Flag by adding a comment to the case.