#!/bin/bash

SMTP_HELO=localhost
SMTP_HOST=localhost
ENV_FROM=${1:?missing FROM address}
ENV_TO=${2:?missing TO address}

function die {
	echo "Error: $1" >&2
	exit 1
}

function expect {
	[ "$1" ] && ( echo "$1" >&3 || die "Could not write to MTA: $1" )
	read line <&3 || die "Could not read from MTA"
	[[ "$line" =~ "$2 " ]] || die "Unexpected response to $1: $line"
}

exec 3<>"/dev/tcp/$SMTP_HOST/25" || die "Could not connect to MTA"
expect "" 220
expect "HELO $SMTP_HELO" 250
expect "MAIL FROM:$ENV_FROM" 250
expect "RCPT TO:$ENV_TO" 250
expect "DATA" 354
cat >&3
expect "." 250
expect "QUIT" 221