Ruby rake style errors when running this code

Question

Here is my code:

#!/usr/bin/env ruby
require 'net/ping'
require 'net/smtp'

# check if host is up
def up?(host)
  check = Net::Ping::External.new(host)
  check.ping?
end

# list of switches to check 
switch_list = [
  ['A ', '192.168.1.1'],
  ['B ', '192.168.1.2'],
  ['C ', '192.168.1.3']
]

failed_switches =[]

switch_list.each do |switch, ip|
  puts "#{switch}" + up?(ip).to_s
  failed_switches << [switch, ip] unless up?(ip)
end

failed_switches.each do |ip| unless failed_switches.empty?
  puts "#{failed_switches}" + up?(ip).to_s + "\n"
end

#email the list of checked and failed swithces
message = <<MESSAGE_END
From: [email protected]
To: [email protected]
Subject: device down!

checked devices:
#{switch_list.map { |switches, ips| 'Device:' + switch + 'IP:' + ip }.join("\n") }

failed devices:
#{failed_switches.map { |switches, ips| 'Device:' + switch + 'IP:' + ip }.join("\n") }

MESSAGE_END
  puts "#{message}"

next unless failed_switches.empty?
Net::SMTP.start('your mail server') do |smtp|
  smtp.send_message message, '[email protected]'
end
end

ERRORS:

Inconsistent indentation detected:
message = <<MESSAGE_END

Unused block argument - line 36 line 39
**|switches**, **ips|** 
Inconsistent indentation detected: line 44
next unless failed_switches.empty?

Inconsistent indentation detected: line 45
Net::SMTP.start('your mail server') do |smtp|

Could someone please help me clear these errors?