Customizable Column That Follows Email Chain

[reberryjr]

I'd like to find a way that a User can add an indicator to an email that sticks with the chain throughout its existence. For example, if an email chain is started, the User can enter a Primary Key into a customizable column, that remains with the email, no matter how many times it's forwarded or responded to.

I tested a customizable column on an email, but the data entered into the column did not stay with the email response.