It is possible to manipulate the behaviour of the JobScheduler e-mail service.
The JobScheduler e-mail service use a stylesheet config/scheduler_mail.xsl for mail transformation.
It is shipped with the standard installation.
create a new stylesheet e.g. config/my_scheduler_mail.xsl as copy of config/scheduler_mail.xsl and edit config/my_scheduler_mail.xsl.
How to change the file type for mail attachments?