elstar.com.au

When I sent emails from the debian server the emails were shown as sent from root@localdomain.localdomain

I am using a fictitious domain name of mydomain.org.au as an example here.

to set the sender to root@mydomain.org.au

I changed the file /etc/mailname which had localdomain.localdomain to
mydomain.org.au

now when i send email using mail fred@gmail.com
the sender shows root@mydomain.org.au

I found the above solution here from the debian documentation page
Chapter 6. Network applications
http://www.debian.org/doc/manuals/debian-reference/ch06.en.html