How to fix postfix: Sender address rejected: need fully-qualified address (in reply to RCPT TO command))?
$mydomain is used as a default value for many other configuration parameters, but it does not set the sender domain.
Take a look to the
$myorigin parameter in
It specifies the domain that appears in mail that is posted on this machine. The default is to use the local machine name,
$myhostname, which defaults to the name of the machine.
For more information, see Postfix basic configuration README