HTML - restrict entry on e-mail replies

We are using Expand-it to automatically send e-mails to service people (Navision 3.60). Is there a way to restrict them from changing certain fields and text when they reply to the e-mails?

As far as I know, there are no email clients which restrict what text the user can put in his or her email, hence the servicepeople can write whatever the heck they want. If you are currently having the service people doing data entry via email, one option might be to have the service person input his or her data through a form on a website. (Or perhaps even though a Navision form, if you have the right software, etc.) The only other option I can think of is to develop a data verification routine which ignores unwanted changes to the wrong fields.