Crystal SMTP Client

README.md

Crystal SMTP Client

Usage

smtp = SmtpClient.new("SMTP_HOST")
begin
  smtp.authenticate("SMTP_USERNAME", "SMTP_PASSWORD")
  smtp.send_email(
    from: "FROM_EMAIL",
    to: "TO_EMAIL",
    subject: "MAIL_SUBJECT",
    body: "MESSAGE"
  )
ensure
  smtp.close
end

smtp.cr

require "base64"
require "openssl"
require "socket"

class SMTPClient
  CRLF = "\r\n"

  def initialize(@host : String, @port : Int32 = 587)
    @socket = TCPSocket.new(@host, @port)
    @socket.tcp_nodelay = true
    @ssl_socket = nil
    read_response
  end

  def authenticate(username : String, password : String)
    send_command("EHLO localhost")
    send_command("STARTTLS")

    @ssl_socket = OpenSSL::SSL::Socket::Client.new(@socket)

    send_command("EHLO localhost")
    send_command("AUTH LOGIN")
    send_command(Base64.strict_encode(username.strip))
    send_command(Base64.strict_encode(password.strip))
  end

  def send_email(from : String, to : String, subject : String, body : String)
    send_command("MAIL FROM:<#{from}>")
    send_command("RCPT TO:<#{to}>")
    send_command("DATA")
    send_command("From: #{from}#{CRLF}To: #{to}#{CRLF}Subject: #{subject}#{CRLF}#{CRLF}#{body}#{CRLF}.#{CRLF}")
  end

  private def send_command(command : String)
    socket = @ssl_socket || @socket
    socket << command << CRLF
    socket.flush
    read_response
  end

  private def read_response : String
    socket = @ssl_socket || @socket
    responses = [] of String

    while line = socket.gets
      line = line.chomp
      responses << line
      break unless line.starts_with?(/\d{3}-/)
    end

    response = responses.last
    raise "SMTP Error: #{response}" if response.starts_with?(/[45]/)
    response
  end

  def close
    send_command("QUIT") rescue nil
    @ssl_socket.try(&.close)
    @socket.close
  end
end