sendmail default sender

I have a lot of servers, let's say our company network is called Loosers, when using this command echo "Subject: testmail $(hostname)" | sendmail -v 'myemail@mycompany.com' I effectively receive an email after a few minutes, but the sender is like hostname@mail.loosers instead of something like noreply.hostname@mail.mycompany.com. Since my predecessor stupidly set the domain to something specifically related to my company, I suppose it is possible to change this email. I browsed my server in /etc/mail/* , then the manual of sendmail, then the Internet in the search of the configuration of sendmail. Nowhere can be found the string looser or mail. I cannot grasp where my predecessor configurated this stupid default sender of sendmail. How can I configure the default sender used by the bash command sendmail?