Mailx command to include sender address

Hi,
I m using mailx to send email. I am using

sender=server name(display name)
echo "body" | mailx -s "subject" -b "bcc address" "to address" -- -f "$sender".

I should get email with sender as only display name. In stead i am getting displayname@server address.

Please suggest

mailx -r "sender name string goes here"   [rest of command options]

Experiment with that and see if you get what you want.