How to send emails using Python and SMTP server

One way to send emails is by using third-party APIs. Another way is to connect to the SMTP server directly. This is the second approach here.

Import the required libraries.

import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
import email.utils as utils
import time
import ssl
from cryptography.fernet import Fernet
from urllib.parse import quote, unquote
from datetime import datetime
import html2text

Create the EmailSenderclass.

Create __init__ and connectmethods as below.

class EmailSender:
    def __init__(self):
        self.smtp_server = "IP or DNS of SMTP Server"
        self.smtp_port = PORT HERE. Probabily 587
        self.username = "USERNAME"
        self.password = "PASSWORD"
        self.sender_name = "ANURAG RANA"
        self.sender_address = "[e-mail]"
        self.domain = "http://anuragrana.in"
        self.smtp_connection = None

   def connect(self):
        if not self.smtp_connection:
            # this line below takes the most time
            self.smtp_connection = smtplib.SMTP(self.smtp_server, self.smtp_port)
            # Create a secure SSL context
            context = ssl.create_default_context()
            # self.smtp_connection.starttls(context=context) # might generate SSL error
            self.smtp_connection.starttls()
            self.smtp_connection.login(self.username, self.password)

Add send method to this class to send the email.

def send_email(self, to_address, subject, body_html):
    msg = MIMEMultipart("alternative")
    msg['message-id'] = utils.make_msgid(domain=self.domain)
    print(msg['message-id'])
    msg["Subject"] = subject
    msg["From"] = f"{self.sender_name} <{self.sender_address}>"
    msg["To"] = to_address
    # Attach the body of the email - text plain
    text_content = html2text.html2text(body_html)
    msg.attach(MIMEText(text_content, "plain"))
    # Attach the body of the email - html
    msg.attach(MIMEText(body_html, "html"))
    # Add the List-Unsubscribe header
    msg.add_header('List-Unsubscribe', unsubscribe_url)
    msg["Date"] = utils.formatdate(localtime=True)
    try:
        response = self.smtp_connection.sendmail(self.sender_address, to_address, msg.as_string())
        print(response)
    except Exception as e:
        print(e)

Important: message-id, List-Unsubscribe, and Date are three headers that are required for better deliverability. Without these headers, your email score will be low. A low email score might lead your email to the spam folder.

MIMEMultipart(“alternative”): This is a subtype of the multipart content type. Using “alternative” indicates that the email message contains multiple representations of the same content, but in different formats. For example, you might have the same email message in both plain text and HTML. The recipient’s email client can then choose which one to display, usually the last part that the client understands. This is useful for ensuring that the recipient can read the email regardless of whether their email client supports plain text or HTML.

Finally, add the close-connection method to the above class.

# close the connection
def close_connection(self):
    if self.smtp_connection:
        self.smtp_connection.quit()
        self.smtp_connection = None

Now in the main code, perform the below steps to send the emails.

Initialize the EmailSender class and call the connect method to create a connection with the SMTP server.

email_sender = EmailSender()
email_sender.connect()

Create an Email Template in an HTML file. Read the content of this file in a variable.

# Read the content of the HTML file
with open("templates/my-first-email-template.html", "r", encoding="utf-8") as file:
    body = file.read()

Create the list of recipients. Let’s call it batch. Iterate over this batch to send emails to everyone individually.

batch = []
# current_batch text file contains email, one email in each line
with open("current_batch.txt", 'r') as file:
    batch = file.readlines()

Now send the emails.

for recipient in batch:
    # sleep for few seconds before each email to avoid flooding the recepient's inbox
    time.sleep(5)
    if not recipient or not recipient.strip():
        continue
    recipient = recipient.strip()
    # check if recipient is in bouncelog
    if recipient in bounced:
        print(f'email in bouncelog. {recipient}')
        continue

    email_sender.send_email(recipient, subject, body)
    print(f'Mail sent to {recipient} - {time.time()}')

---

We will discuss the bounce log and how to parse the POSTFIX logs for bounced emails in another article.

Connect with me if you want to set up a fully functional new email Postfix SMTP server to send and receive emails.

https://anuragrana.in

Follow me on Medium: https://medium.com/@03A_R/custom-parameter-logging-in-postfix-mta-logs-30c269c681b2