When creating a new job based on a job with the email ext plugin configured, the configuration gest lost during the copy process.
same behaviour can be observed with custom plugin we developed inhouse which creates jobs based on a template job for each feature branch in git.
I can't replicate this. I created a job, setup some stuff in email-ext and saved. Then I created a new item and did a copy from the original item. All of the settings I had changed in the original job were in the new job that was a copy.