A Python script to send emails

mailer.py

#! /usr/bin/python


import argparse
import logging
import os
import smtplib
import sys


def get_receiver_emails(_file):
    """Reads list of emails from a file.

    The list of emails are seperated by a new line.
    """
    emails = []
    with _file as f:
        raw_emails = f.read()
        emails = raw_emails.split()
    return emails


def read_message(_file):
    """Reads email message and returns it."""
    message = ""
    with _file as f:
        message = f.read()
    return message


def load_context():
    """Reads environment variable and returns the context."""
    context = {
        "host": os.environ.get("SMTP_HOST", "localhost"),
        "port": os.environ.get("SMTP_PORT", 465),
        "username": os.environ.get("SMTP_USERNAME", "test@test.com"),
        "password": os.environ.get("SMTP_PASSWORD", "test"),
        "from_address": os.environ.get("FROM_EMAIL", "test@test.com"),
    }
    return context


def start(context):
    """Starts the process of sending mails."""

    with smtplib.SMTP_SSL(host=context["host"], port=context["port"]) as server:
        try:
            logging.debug("Connecting to the SMTP server.")
            server.login(context["username"], context["password"])
            logging.debug("Connected to the SMTP server.")
        except smtplib.SMTPAuthenticationError as e:
            sys.exit(2)

        for to_address in context["to_addresses"]:
            try:
                logging.debug(f"From email {context['from_address']}")
                logging.debug(f"To email {to_address}")
                logging.debug(f"Message {context['message']}")
                server.sendmail(
                    context["from_address"],
                    to_address,
                    context["message"]
                )
                logging.info(f"Mail sent to {to_address}")
            except smtplib.SMTPSenderRefused as e:
                logging.error("Error: Connection refused by the SMTP server.")
                sys.exit(2)
            except smtplib.SMTPDataError as e:
                logging.error("Error: Invalid email body received.")
                sys.exit(2)


def init_logger(log_level):
    """Initialize logger."""
    level = getattr(logging, log_level.upper())
    logging.basicConfig(level=level)


if __name__ == "__main__":
    description = "A script to send individual mails to the receptions."

    parser = argparse.ArgumentParser(description=description)
    parser.add_argument(
        'addresses',
        type=open,
        help='File containing list of email addresses separated by new-line.'
    )
    parser.add_argument(
        'message',
        type=open,
        help='File containing email body in plain text.'
    )
    parser.add_argument(
        '--log-level',
        '-l',
        type=str,
        default="info",
        choices=["debug", "info", "warning", "error", "critical"]
    )
    args = parser.parse_args()
    init_logger(args.log_level)

    context = load_context()
    context["to_addresses"] = get_receiver_emails(args.addresses),
    context["message"] = read_message(args.message)
    start(context)