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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

body: System {{ ansible_hostname }} has been successfully provisioned.
    secure: always
- name: Sending an e-mail using StartTLS to the remote machine
  mail:
    host: localhost
    port: 25
    to: John Smith <john.smith@example.com>
    subject: Ansible-report
    body: System {{ ansible_hostname }} has been successfully provisioned.
    secure: starttls
'''
import os
import smtplib
import ssl
import traceback
from email import encoders
from email.utils import parseaddr, formataddr
from email.mime.base import MIMEBase
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.header import Header
from ansible.module_utils.basic import AnsibleModule
from ansible.module_utils.six import PY3
from ansible.module_utils._text import to_native
def main():
    module = AnsibleModule(
        argument_spec=dict(
            username=dict(type='str'),
            password=dict(type='str', no_log=True),
            host=dict(type='str', default='localhost'),