Return address is your incoming email. To let a letter be sent not from a system address (firstname.lastname@example.org), but from a custom address, you need toset up an email for mailings sending.
You can change a return address.
To do it change it in “Settings” tab in “Return address” field:
Mind, that if you change a return address, a response will come to this particular address you’ve inserted. To get a response in GetCourse you need to set up readdressing from the specified address to the address of your incoming email in your account: