Python - Sending Email

An application that handles and delivers e-mail over the Internet is called a "mail server". Simple Mail Transfer Protocol (SMTP) is a protocol, which handles sending an e-mail and routing e-mail between mail servers. It is an Internet standard for email transmission.

Python provides smtplib module, which defines an SMTP client session object that can be used to send mails to any Internet machine with an SMTP or ESMTP listener daemon.

Python smptlib.SMTP() Function

To send an email, you need to obtain the object of SMTP class with the following function −

import smtplib

smtpObj = smtplib.SMTP( [host [, port [, local_hostname]]] )

Here is the detail of the parameters −

  • host − This is the host running your SMTP server. You can specify IP address of the host or a domain name like This is an optional argument.

  • port − If you are providing host argument, then you need to specify a port, where SMTP server is listening. Usually this port would be 25.

  • local_hostname − If your SMTP server is running on your local machine, then you can specify just localhost as the option.

The Python smtpd Module

The smtpd module that comes pre-installed with Python has a local SMTP debugging server. You can test email functionality by starting it. It doesn't actually send emails to the specified address, it discards them and prints their content to the console. Running a local debugging server means it's not necessary to deal with encryption of messages or use credentials to log in to an email server.

You can start a local SMTP debugging server by typing the following in Command Prompt −

python -m smtpd -c DebuggingServer -n localhost:1025


The following program sends a dummy email with the help of smtplib functionality.

import smtplib

def prompt(prompt):
   return input(prompt).strip()
fromaddr = prompt("From: ")
toaddrs = prompt("To: ").split()
print("Enter message, end with ^D (Unix) or ^Z (Windows):")

# Add the From: and To: headers at the start!
msg = ("From: %s\r\nTo: %s\r\n\r\n"
   % (fromaddr, ", ".join(toaddrs)))
while True:
      line = input()
   except EOFError:
   if not line:
   msg = msg + line
print("Message length is", len(msg))
server = smtplib.SMTP('localhost', 1025)
server.sendmail(fromaddr, toaddrs, msg)

Basically we use the sendmail() method, specifying three parameters −

  • The sender − A string with the address of the sender.

  • TheThe receivers − A list of strings, one for each recipient.

  • TheThe message − A message as a string formatted as specified in the various RFCs.

We have already started the SMTP debugging server. Run this program. User is asked to input the sender's ID, recipients and the message.

Enter message, end with ^D (Unix) or ^Z (Windows):
Hello World

The console reflects the following log −

reply: retcode (250); Msg: b'OK'
send: 'rcpt TO:<>\r\n'
reply: b'250 OK\r\n'
reply: retcode (250); Msg: b'OK'
send: 'data\r\n'
reply: b'354 End data with <CR><LF>.<CR><LF>\r\n'
reply: retcode (354); Msg: b'End data with <CR><LF>.<CR><LF>'
data: (354, b'End data with <CR><LF>.<CR><LF>')
send: b'From:\r\nTo:\r\n\r\nHello
reply: b'250 OK\r\n'
reply: retcode (250); Msg: b'OK'
data: (250, b'OK')
send: 'quit\r\n'
reply: b'221 Bye\r\n'
reply: retcode (221); Msg: b'Bye'

The terminal in which the SMTPD server is running shows this output

---------- MESSAGE FOLLOWS ----------
b'X-Peer: ::1'
b'Hello World'
------------ END MESSAGE ------------

Sending an HTML e-mail using Python

When you send a text message using Python, then all the content are treated as simple text. Even if you include HTML tags in a text message, it is displayed as simple text and HTML tags will not be formatted according to HTML syntax. But Python provides option to send an HTML message as actual HTML message.

While sending an e-mail message, you can specify a Mime version, content type and character set to send an HTML e-mail.


Following is the example to send HTML content as an e-mail. Try it once −

import smtplib

message = """From: From Person <>
To: To Person <>
MIME-Version: 1.0
Content-type: text/html
Subject: SMTP HTML e-mail test

This is an e-mail message to be sent in HTML format

<b>This is HTML message.</b>
<h1>This is headline.</h1>

   smtpObj = smtplib.SMTP('localhost')
   smtpObj.sendmail(sender, receivers, message)         
   print "Successfully sent email"
except SMTPException:
   print "Error: unable to send email"

Sending Attachments as an E-mail

To send an e-mail with mixed content requires to set Content-type header to multipart/mixed. Then, text and attachment sections can be specified within boundaries.

A boundary is started with two hyphens followed by a unique number, which cannot appear in the message part of the e-mail. A final boundary denoting the e-mail's final section must also end with two hyphens.

Attached files should be encoded with the pack("m") function to have base64 encoding before transmission.


Following is the example, which sends a file /tmp/test.txt as an attachment. Try it once −

import smtplib
import base64

filename = "/tmp/test.txt"

# Read a file and encode it into base64 format
fo = open(filename, "rb")
filecontent =
encodedcontent = base64.b64encode(filecontent)  # base64

sender = ''
reciever = ''


body ="""
This is a test email to send an attachment.
# Define the main headers.
part1 = """From: From Person <>
To: To Person <>
Subject: Sending Attachment
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary=%s
""" % (marker, marker)

# Define the message action
part2 = """Content-Type: text/plain

""" % (body,marker)

# Define the attachment section
part3 = """Content-Type: multipart/mixed; name=\"%s\"
Content-Disposition: attachment; filename=%s

""" %(filename, filename, encodedcontent, marker)
message = part1 + part2 + part3

   smtpObj = smtplib.SMTP('localhost')
   smtpObj.sendmail(sender, reciever, message)
   print "Successfully sent email"
except Exception:
   print "Error: unable to send email"

Using gmail SMTP

Let us look at the script below which uses Google's smtp mail server to send an email message.

First of all SMTP object is set up using gmail's smtp server and port 527. The SMTP object then identifies itself by invoking ehlo() command. We also activate Transport Layer Security to the outgoing mail message.

Next the login() command is invoked by passing credentials as arguments to it. Finally the mail message is assembled by attaching it a header in prescribed format and it is sent using sendmail() method. The SMTP object is closed afterwards.

import smtplib
content="Hello World"
mail=smtplib.SMTP('', 587)
header='To:'+receipient+'\n'+'From:' \
mail.sendmail(sender, recipient, content)

Before running above script, sender's gmail account must be configured to allow 'less secure apps'. Visit following link. Set the shown toggle button to ON.

toggle button

If everything goes well, execute the above script. The message should be delivered to the recipient's inbox.