import hmac
import time
import requests
import hashlib
from ordereddict import OrderedDict
 
def encode_param_without_escaping(key, value):
    if isinstance(value, list):
        return '&'.join([key + '[]=' + item for item in value])
    else:
        if isinstance(value, dict):
            value = json.dumps(value)
    return "{key}={value}".format(key=key, value=value)
 
timestamp = int(time.time())
data = {
    "auth_key": 'SUA CHAVE PÚBLICA',
    "auth_timestamp": timestamp,
    "auth_version": "1.0",
    "recipient_list": [
		"Destinatario1 <destinatario1@exemplo.com>", "<destinatario2@exemplo.com>"
    ],
    'message_text': 'Exemplo',
    "from": 'Remetente <remetente@exemplo.com>',
    "subject": "Exemplo"
}
params_dict = OrderedDict(sorted(data.items()))
params_list = []
for key, value in params_dict.iteritems():
    params_list.append(encode_param_without_escaping(key, value))
msg_default = '&'.join(params_list)

hmac_dict = {
    'key': 'SUA CHAVE PRIVADA',
    'digestmod': hashlib.sha256
}
hmac_dict.update({'msg': 'POST\n/api/send_mail/\n' + msg_default})
auth_signature_post_text = hmac.new(**hmac_dict).hexdigest()

url_base = '{0}{1}?auth_key={2}&auth_timestamp={3}&auth_version=1.0&auth_signature={4}'
url_post_text = url_base.format(
    'http://postman.alterdata.com.br', '/api/send_mail/', 'SUA CHAVE PÚBLICA', timestamp, auth_signature_post_text
)
response = requests.post(url_post_text, {}, params_dict)