We see other companies platforms with the ability to pre-append a notice at the top of the body of the email. It might read something like the following.
"Caution: This email originated outside of the company. Review the email and do not click on any llinks or attachments unless you believe this email is valid and the From address is correct."
We have also seen the ability to be able to color/bold, etc. parts of the email to make it more readable.
With all of the phishing going on and this representing over 90% of compromises in companies, I have to believe other customers are asking for this.
This is not possible with our email system or cllient and why we would like to see this enhancement made at this level. The subject tagging is not enough and would not be noticeable on a mobile device.