Could you please check whether you are having logic to hold all mail related information in Data-Corr-Email shadow page, that page is getting deferred save in activity via which you are sending mail and then you are invoking CorrAttach activity to establish link.
You could refer SendSimpleEmail activity to know what all values needs to get populated in Data-Corr-Email shadow page
Because in back-end pega will just have link between the work object and Data-Corr-Email entry instance, this link is responsible for displaying triggered mail in work object audit.
Attached screen-shot, please use it for reference.