Python send mail to multiple recipients using SMTP server

In this post, you will learn how to write Python code to send email to multiple recipients using the SMTP server.

SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol of the Internet standard for electronic mail transmission from the sender to one or more recipients. To connect to an SMTP mail server, we need the following details HOSTNAME, USERNAME, PASSWORD and PORT NUMBER.

Python provides the in-built module smtplib to send email using SMTP Server. There is no extra installation required. So first, we need to import this at the top of the script and define a SMTP client session object that can be used to send mail.

import smtplib

Python Connection to SMTP Server

The SMTP object encapsulates a SMTP connection. It has the following syntax-

smtplib.SMTP([host, port, local_hostname, timeout)

host- The host name of your SMTP server. We can specify the IP address of the host or a domain name.
port- The port number where the SMTP server is listening. Generally, this port would be 25.
local_hostname- If your STMP server is running on the local machine, then we can just specify the 'localhost'.
timeout- It is an optional parameter and specifies a timeout in seconds for blocking operations.

SMTP Authentication

STMP Authentication requires login to the SMTP Server. It has the following syntax-

SMTP.login(username, password)

The arguments are the username and password to authenticate with the server.

Start TLS

We should start the TLS for a security reason. It will encrypt all the commands that follow this.

starttls()

Send Mail

The sendmail() function is used to send mail to the recipients. It has the following syntax-

sendmail(from, to, msg)

Here, the from is the sender mail address and the to is the recipient mail address, and the msg contains messages to be sent in the string.

Quit the SMTP connection

At last, we should terminate the SMTP session and close the connection using an SMTP QUIT() command.

Python code to send mail

Here is the complete code in Python to send mail to multiple recipients using the SMTP Mail Server.

#Python code to send mail
import smtplib 

try:
    # Set sender mail, receivers mail and messages
    sender_mail = "This email address is being protected from spambots. You need JavaScript enabled to view it."
    receivers_mail = ['receiver1@domain', 'receiver2@domain']
    to = ", ".join(receivers_mail)
    message = """Subject: Python testing mail

            This mail is sent using Python SMTP."""
    
    # Make SMTP connection
    obj = smtplib.SMTP('smtp.gmail.com', 587) 
  
    # secure with TLS
    obj.starttls() 
  
    # Mail Server Authentication
     obj.login(USRENAME, PASSWORD) 
  
    # sending the mail 
    obj.sendmail(sender_mail, to, message) 
    print("Mail sent successfully.")
    
    # terminating the session 
    obj.quit()
    
except Exception:
    print("Mail delivery failed.")

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