Running this with mailcatcher results in a "503 MAIL already given"

mail_test.rb

#!/usr/bin/env ruby

require 'net/smtp'
require 'time'

def send_message(smtp, from, to)
  msg = %{From: #{from}
To: #{to}
Subject: test message
Date: #{Time.now.rfc2822}
Message-Id: <#{Time.now.to_f}@example.com>

This is a test message.
}
  smtp.send_message(msg, from, to)
end

Net::SMTP.start('localhost', 1025) do |smtp|
  send_message(smtp, 'from@example.com', 'to1@example.com')
  send_message(smtp, 'from@example.com', 'to2@example.com')
end