Simple script to auto-reply mails

example-config.yml

from: any@example.com

body: "Invalid mail"

include_source: true

mail-auto-reply.rb

#!/usr/bin/ruby

require 'tmail'
require 'yaml'
require 'net/smtp'

config = YAML.load(File.read(ARGV.first || "/etc/mail-autoreply.yml"))
raw_mail = STDIN.read

mail = TMail::Mail.parse(raw_mail)

if mail.from.first == config["from"]
    # Ignore "self" emails
    exit 0
end

response = TMail::Mail.new
response.subject = config["subject"] || "Re: #{mail.subject}"
response.from = config["from"]
response.to = mail.from.first
response.in_reply_to = mail.message_id
response.disposition = "inline"
response.date = Time.now

body = TMail::Mail.new
body.content_type = "text/plain; charset=UTF-8"
body.body = config["body"]
body.disposition = "inline"
response.parts << body

if config["include_source"]
    original_mail = TMail::Mail.new
    original_mail.content_type = "message/rfc822"
    original_mail.body = raw_mail.sub(/\AFrom .*?$/, '').sub(/\A\s+/, '')
    original_mail.disposition = "inline"
    response.parts << original_mail
end

Net::SMTP.start('localhost', 25) do |smtp|
    smtp.send_message response.to_s, response.from, response.to
end