Python E-Mail mit Text und Anhang senden

Ich habe ein Skript zum Sichern meiner Neo4J-Datenbank geschrieben.

Am Ende des Sicherungsvorgangs werden E-Mails an den DB-Administrator gesendet

Die E-Mail ohne die erhalten message_body.

Dies ist der Code:

message = MIMEMultipart('alternative')
message['To'] = "Database Admin <%s>" % _receiver
message['From'] = "Pico.buzz Graph Database <%s>" % _sender
if not log.is_error():
    message['Subject'] = "Graph DB Backup Finished Successfully"
    message_body = 'Successfully backup email. Please see review log file'
else:
    message['Subject'] = "ATTENTION: ERROR! Graph DB Backup Failed"
    message_body = 'An error occur during backup. please review log'
instance_name = aws.get_instance_name()
instance_details = "Instance Id: %s\nPrivate IP Address: %s" % (aws.get_instance_id(), aws.get_instance_ip())
if instance_name is not None:
    instance_details = """Instance Name: %s\n%s""" % (instance_name, instance_details)
message_body = "%s\n\n%s" % (message_body, instance_details)
content = MIMEText(message_body, 'plain')
message.attach(content)
message.attach(_get_log_file())
smtp = smtplib.SMTP('localhost')
smtp.sendmail(_sender, _receiver, message.as_string())
log.info(__name__, "Successfully sent email to: %s" % _receiver)

Irgendeine Idee warum?