Django + gmail + nginx + allauth: unable to send email (but works on localhost)

I’m working on a Django application with a registration by email with confirmation (using allauth). When the user create a new account, he receive a confirmation email on his email box. All works perfect on my local machine. But when I try it on my digital ocean server (Ubuntu 16.04), the email is not sent. My Django email settings are:

EMAIL_USE_TLS = True
EMAIL_HOST = 'smtp.gmail.com'
EMAIL_HOST_USER = "my_email@gmail.com"
EMAIL_HOST_PASSWORD = "my_password"
EMAIL_PORT = 587
EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'

My error.log file is empty, it seems like there is no error from the Python server, or maybe my logfile is not correctly configured:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'file': {
            'level': 'ERROR',
            'class': 'logging.FileHandler',
            'filename': './error.log',
        },
    },
    'loggers': {
        'django': {
            'handlers': ['file'],
            'level': 'ERROR',
            'propagate': True,
        },
    },
}

I tried to allow access to my Google account using external application with this link https://accounts.google.com/b/0/DisplayUnlockCaptcha but it doesn’t change anything.

I tried to change SMTP port to 465 like described here: https://www.digitalocean.com/community/tutorials/how-to-use-google-s-smtp-server, but same thing, no change.

Does somebady have an idea?