Vitaly Sotnikov

pip install Flask-Mail

from flask_mail import Mail
from flask.ext.mail import Message

mail = Mail(app)


def send_email(subject, sender, recipients, text_body, html_body):
    msg = Message(subject, sender=sender, recipients=recipients)
    msg.body = text_body
    msg.html = html_body
    mail.send(msg)


def send_post(email, post):
	  send_email('This is a new post',
		'admin@example.com',
		[email],
		post,
		'<p>' + post + '</p>')

третий параметр это список т.е можно подкинуть список с несколькими адресами.