default value of relayhost in postfix main.cf

I am puzzled to see that the "relayhost" parameter of my /etc/postfix/main.cf has been empty all the while sending mail using mailx has been working fine. Does the default value of "relayhost" default to "mailhost"? since "mailhost" is my organization's SMTP server's name.

I am running Suse Leap 15.1