$ sudo cp /etc/postfix/main.cf{,.org} $ sudo vi /etc/postfix/main.cf $ sudo diff -u /etc/postfix/main.cf{.org,} --- /etc/postfix/main.cf.org 2013-01-20 06:44:10.831132999 +0000 +++ /etc/postfix/main.cf 2013-01-20 12:21:11.669057494 +0000 @@ -74,6 +74,7 @@ # #myhostname = host.domain.tld #myhostname = virtual.domain.tld +myhostname = mail.example.com # The mydomain parameter specifies the local int