From log:
Running newaliases newaliases: warning: valid_hostname: invalid character 40(decimal): ubuntu.(null) newaliases: fatal: file /etc/postfix/main.cf: parameter myhostname: bad parameter value: ubuntu.(null) dpkg: error processing postfix (--configure): subprocess installed post-installation script returned error exit status 75
From log:
Running newaliases main.cf: parameter myhostname: bad parameter value: ubuntu.(null)
newaliases: warning: valid_hostname: invalid character 40(decimal): ubuntu.(null)
newaliases: fatal: file /etc/postfix/
dpkg: error processing postfix (--configure):
subprocess installed post-installation script returned error exit status 75