TLM Synaptic Error

(Reading database ... 310659 files and directories currently installed.)
Removing bsd-mailx ...
Purging configuration files for bsd-mailx ...
Removing cardstories ...
 * Stopping cardstories... not running
Restarting nginx: nginx.
Purging configuration files for cardstories ...
Restarting nginx: nginx.
Processing triggers for man-db ...
Processing triggers for ureadahead ...
Setting up postfix (2.8.5-2~build1) ...

Postfix configuration was not changed.  If you need to make changes, edit
/etc/postfix/main.cf (and others) as needed.  To view Postfix configuration
values, see postconf(1).

After modifying main.cf, be sure to run '/etc/init.d/postfix reload'.

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
No apport report written because MaxReports is reached already
                                                              Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
Errors were encountered while processing:
 postfix
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install.  Trying to recover:
Setting up postfix (2.8.5-2~build1) ...

Postfix configuration was not changed.  If you need to make changes, edit
/etc/postfix/main.cf (and others) as needed.  To view Postfix configuration
values, see postconf(1).

After modifying main.cf, be sure to run '/etc/init.d/postfix reload'.

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
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
Errors were encountered while processing:
 postfix