Test SMTP with telnet using bash.

testsmtp.sh

#!/bin/bash

#
# Solution based on https://stackoverflow.com/a/11988455/119829
# Thank you balanv.
#

base_domain=test.example.com;

command -v telnet >/dev/null 2>&1 || { echo >&2 "I require telnet but it's not installed.  Aborting."; exit 1; }

[ "$1" ] || { echo >&2 "arg 1 (domain/ip4) cannot be empty."; exit 1; }

[ "$2" ] || { echo >&2 "arg 2 (port) cannot be empty."; exit 1; }

echo "Sending test message from [ $base_domain ] to [ $1 $2 ] via telnet...\n";

telnet $1 $2 <<EOF
helo $1 $2
mail from:<no-reply@$base_domain>
rcpt to:<test_script@$base_domain>
data
From: developer@$base_domain
Subject: This is a test message.

This is a test message from the linux command line. If you recieve this message then your SMTP server is configured correctly.
This tool only works with unencrypted connects.
.
quit
EOF