Python - Sending SMTP Email - Python Tutorials

In this chapter, I will teach you how to use Python to send emails. So we would write a simple Python program to send emails to Yahoo, Gmail etc.

How SMTP Works
Sending an Email
How Email is Sent
Sending HTML Email in Python
Including Attachment to Email

1. How SMTP Works

SMTP stands for Simple Mail Transfer Protocol. You use SMTP to send relay emails between mail servers.

The smtplib module is used for this purpose. So you need to import it. This module defines something called ‘SMTP client session object’. This is an object used for sending email to any mail server on the Internet.

To create an SMTP session object, you use the following syntax:

import smtplib

smtpObject = smtplib.SMTP(host, portnumber, localhostname)

The SMTP function takes three parameters: host, portnumber and local_hostname

host – This is the host running SMTP server. You can either specify the computer name, domain name or IP address

portnumber: This is the port on the server where the SMTP is listening. You can typically use port 25 as the portnumber.

localhostname: This is a situation where the SMTP server is your local machine. In this case, the localhostname is just localhost (or your computer name)

2. Sending an Email

After creating an SMTP session object, you need to use sendmail method. The sendmail method is an instance method used to send and email.

This method takes three parameters:

sender – This is a string of the sender email address

recipients – List of recipient email addresses

message – A string that specified To, subject and body of the email

The code below sends an email to the specified email address

import smtplib

sender = '[email protected]'
recipients = ['[email protected]']

message = """From: Sender Name <[email protected]>
To: Recipient Name <[email protected]>
Subject: Test Email

This is a sample email sent from Python
"""

try:
    smtpObject = smtplib.SMTP('smtp.gmail.com', 587)
    smtpObject.sendmail(sender, recipients, message)
    print("Email has been sent")
except:
    print("Error Occured: Email Sending failed")

3. How Email is Sent

First, we import the smtplib. Then we define a sender and a list of recipients. Then we define a multiline message. Note that the message specifies the Sender, the Recipient and the Subject. Now, these three items make up the header and they are each place in separate line.

You can get the hostname from the particular host.

4. Sending HTML Email in Python

A HTML email is different from plain-text email described above. So this means, you can format using html tags. Even if you use html, everything would be displayed as plain text. Therefore to use formatted text which is called HTML email, you need to add two more headers to the email message.

These headers are: MIME-Version and Content-type. The mime version is set to 1.0 while the Content-type is set to text/html.

See example below, where we have modified the original code to support HTML email.

import smtplib

sender = '[email protected]'
recipients = ['[email protected]']

message = """From: Sender Name <[email protected]>
To: Recipient Name <[email protected]>
Subject: Test Email
MIME-Version: 1.0
Content-type: text/html

This is a sample email sent from Python
"""

try:
    smtpObject = smtplib.SMTP('localhost')
    smtpObject.sendmail(sender, recipients, message)
    print("Email has been sent")
except:
    print("Error Occured: Email Sending failed")

5. Including Attachments to Email

Just like you can attach files when sending email, you can do same in Python. So to do this, you simple change the Content-type to multipart/mixed.

After you do this, you also need to specify the text and attachment sections within boundaries.

A boundary begins with two hyphens followed by a number. The number must be unique. You need to fetch the attachment using normal File Operation. I recommend you review Reading from files.

The attached file must be encoded in base64. You can encode using the pack(“m”) function.

The complete code for sending an attachment is given below:

import smtplib
import base64

filename = "D/test.txt"

# Read  a file from the file system
fo = open(filename, "rb")
filecontent = fo.read()
encodedcontent = base64.b64encode(filecontent)

sender = '[email protected]'
reciever = '[email protected]'

marker = "MARKER"

body = """
This an email sent with an attachment from kindsonthegenius.com/python.
"""
# Main headers is defined here.
section1 = """From: From Person <[email protected]>
To: To Person <[email protected]>
Subject: Sending Attachment
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary=%s
--%s
""" % (marker, marker)

# The message action is defined here
section2 = """Content-Type: text/plain
Content-Transfer-Encoding:8bit

%s
--%s
""" % (body,marker)

# The attachment is defined here
section3 = """Content-Type: multipart/mixed; name=\"%s\"
Content-Transfer-Encoding:base64
Content-Disposition: attachment; filename=%s

%s
--%s--
""" %(filename, filename, encodedcontent, marker)
message = section1 + section2 + section3

try:
    smtpObject = smtplib.SMTP('localhost')
    smtpObject.sendmail(sender, reciever, message)
    print("Email has been sent successfully")
except Exception:
    print("Error occured: Email sending failed")