I installed mailutils just yesterday and today spent hours trying to set the mail variable "savekeep" to True. The mailutils documentation is poor but I got things to work after finding
2.4.7 Personal and System-wide Configuration Files. So then the task is to find out how to write the settings in a mailrc file. You can refer to .mailrc File Format on the ibm.com website.
You need to create the file ~you/.mailrc for user configuration or /etc/mail.rc for system wide configuration. Here is what you need to write in the file to set "savekeep" and "askcc".
set askcc=False;
set keepsave=True;