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##### SUMMARY
mail module does not send email with Date header. It should send email with "Date" header automatically without any manual email header manipulation.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
mail

##### ANSIBLE VERSION
```
ansible 2.8.1
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/home/yclee/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/dist-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.15+ (default, Nov 27 2018, 23:36:35) [GCC 7.3.0]
```

##### CONFIGURATION
(None)

##### OS / ENVIRONMENT
Ubuntu 18.04

##### STEPS TO REPRODUCE
N/A

##### EXPECTED RESULTS
email should have Date headers

##### ACTUAL RESULTS
email did not  have Date headers and I have to manually insert it

part = MIMEText(body + "\n\n", _subtype=subtype, _charset=charset)
    msg.attach(part)
    
    
    for filename in attach_files:
        try:
            part = MIMEBase('application', 'octet-stream')
            with open(filename, 'rb') as fp:
                part.set_payload(fp.read())
            encoders.encode_base64(part)
            part.add_header('Content-disposition', 'attachment', filename=os.path.basename(filename))
            msg.attach(part)
        except Exception as e:
            module.fail_json(rc=1, msg="Failed to send mail: can't attach file %s: %s" %
                             (filename, to_native(e)), exception=traceback.format_exc())
    composed = msg.as_string()
    try:
        result = smtp.sendmail(sender_addr, set(addr_list), composed)
    except Exception as e:
        module.fail_json(rc=1, msg="Failed to send mail to '%s': %s" %
                         (", ".join(set(addr_list)), to_native(e)), exception=traceback.format_exc())
    smtp.quit()
    if result:
        for key in result:
            module.warn("Failed to send mail to '%s': %s %s" % (key, result[key][0], result[key][1]))
        module.exit_json(msg='Failed to send mail to at least one recipient', result=result)
    module.exit_json(msg='Mail sent successfully', result=result)
if __name__ == '__main__':
    main()