How to send email using simple SMTP commands via Gmail?

Question

For educational purposes, I need to send an email through an SMTP server, using SMTP\'s fundamental and simple rules.

I was able to do that using smtp4dev. I

Answer 1

Based on the existing answers, here's a step-by-step guide to sending automated e-mails over SMTP, using a GMail account, from the command line, without disclosing the password.

Requirements

First, install the following software packages:

• Expect
• OpenSSL
• Core Utils (base64)

These instructions assume a Linux operating system, but should be reasonably easy to port to Windows (via Cygwin or native equivalents), or other operating system.

Authentication

Save the following shell script as authentication.sh:

#!/bin/bash

# Asks for a username and password, then spits out the encoded value for
# use with authentication against SMTP servers.

echo -n "Email (shown): "
read email
echo -n "Password (hidden): "
read -s password
echo

TEXT="\0$email\0$password"

echo -ne $TEXT | base64

Make it executable and run it as follows:

chmod +x authentication.sh
./authentication.sh

When prompted, provide your e-mail address and password. This will look something like:

Email (shown): bob@gmail.com
Password (hidden): 
AGJvYkBnbWFpbC5jb20AYm9iaXN0aGViZXN0cGVyc29uZXZlcg==

Copy the last line (AGJ...==), as this will be used for authentication.

Notification

Save the following expect script as notify.sh (note the first line refers to the expect program):

#!/usr/bin/expect

set address "[lindex $argv 0]"
set subject "[lindex $argv 1]"
set ts_date "[lindex $argv 2]"
set ts_time "[lindex $argv 3]"

set timeout 10
spawn openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof 

expect "220" {
  send "EHLO localhost\n"

  expect "250" {
    send "AUTH PLAIN YOUR_AUTHENTICATION_CODE\n"

    expect "235" {
      send "MAIL FROM: \n"

      expect "250" {
        send "RCPT TO: <$address>\n"

        expect "250" {
          send "DATA\n"

          expect "354" {
            send "Subject: $subject\n\n"
            send "Email sent on $ts_date at $ts_time.\n"
            send "\n.\n"

            expect "250" {
                send "quit\n"
            }
          }
        }
      }
    }
  }
}

Make the following changes:

1. Paste over YOUR_AUTHENTICATION_CODE with the authentication code generated by the authentication script.
2. Change YOUR_EMAIL_ADDRESS with the e-mail address used to generate the authentication code.
3. Save the file.

For example (note the angle brackets are retained for the e-mail address):

send "AUTH PLAIN AGJvYkBnbWFpbC5jb20AYm9iaXN0aGViZXN0cGVyc29uZXZlcg==\n"
send "MAIL FROM: \n"

Lastly, make the notify script executable as follows:

chmod +x notify.sh

Send E-mail

Send an e-mail from the command line as follows:

./notify.sh recipient@domain.com "Command Line" "March 14" "15:52"