Running SMTP server in development environment with python

2020-09-01 17:02:29 +0000

Sometimes we need to test a code responsible for send emails, did you know that’s possible to create your own email server with a single command? And all do you need is the python.

The python standard library has a lot of useful things, like the smtpd that allow us to run a simple SMTP server on our own machine in seconds.

LISTEN_ON_ADDRESS=localhost; LISTEN_ON_PORT=2500 && \
python -m smtpd -n -d -c DebuggingServer ${LISTEN_ON_ADDRESS}:${LISTEN_ON_PORT}

You’ll see something like this:

DebuggingServer started at Tue Sep  1 18:10:46 2020
	Local addr: ('localhost', 2500)
	Remote addr:('localhost', 25)

You can test with your code or using telnet:

$ telnet 192.168.0.145 2500
Trying 192.168.0.145...
Connected to 192.168.0.145.
Escape character is '^]'.
220 y740 Python SMTP proxy version 0.3
HELO demo.example.com
250 y740
mail from: user@example.com
250 OK
rcpt to: another.user@example.com
250 OK
data
354 End data with <CR><LF>.<CR><LF>
Hey 
This is my test email

Thanks
.
250 OK
quit
221 Bye
Connection closed by foreign host.

On the smtpd terminal you will see something like that:

Incoming connection from ('192.168.0.145', 42860)
Peer: ('192.168.0.145', 42860)
Data: b'HELO demo.example.com'
Data: b'mail from: user@example.com'
===> MAIL from: user@example.com
sender: user@example.com
Data: b'rcpt to: another.user@example.com'
===> RCPT to: another.user@example.com
recips: ['another.user@example.com']
Data: b'data'
Data: b'Hey\r\nThis is my test email\r\n\r\nThanks'
---------- MESSAGE FOLLOWS ----------
b'Hey'
b'This is my test email'
b'X-Peer: 192.168.0.145'
b''
b'Thanks'
------------ END MESSAGE ------------
Data: b'quit'