We have the need to remove a custom message (injected by our firewall) from all the emails received from our customers.

Right now the only way we have are exploiting the extension point: 

Work-Channel-Triage-Email.MapEmailToEmailTriageExtn 

and we had to change the Email Service > Request > Message data > Handle HTML Content from "As HTML attachment" to "Inline - Prefer HTML", which is now giving us a some troubles, because some of the emails are NOT correctly detected as HTML!

Is there another extension point that we can keep the old configuration "As HTML attachment" and change the email body?

With this setting we have noticed that if we replace the text in the previous extension point, then the body is sourced from the attachment, instead of the one in the property.