Why can't the block see my variable?
post "/email/send" do

  @recipient = params[:email]

  Mail.deliver do
    to @recipient # throws error as this is undefined
    from 'server@domain.com'
    subject 'testing sendmail'
    body 'testing sendmail'
  end

  erb :email_sent

end

post "/email/send" do

  Mail.deliver do
    to 'me@domain.com'
    from 'server@domain.com'
    subject 'testing sendmail'
    body 'testing sendmail'
  end

  erb :email_sent

end

recipient = params[:email]
Mail.deliver do
    to recipient # 'recipient' is a local variable, not a method, not an instance variable
...
end

Mail.deliver do
  to @recipient # throws error as this is undefined
  from 'server@domain.com'
  subject 'testing sendmail'
  body 'testing sendmail'
end

Mail.new(
  to:      @recipient,
  from:    'server@domain.com',
  subject: 'testing sendmail',
  body:    'testing sendmail'
).deliver!

Mail.new(
  :to      => @recipient,
  :from    => 'server@domain.com',
  :subject => 'testing sendmail',
  :body    => 'testing sendmail'
).deliver!

pry(main)> Mail.new(
pry(main)* to: 'me@domain.com',
pry(main)* from: 'me@' << `hostname`.strip,
pry(main)* subject: 'test mail gem',
pry(main)* body: 'this is only a test'
pry(main)* ).deliver!
=> #<Mail::Message:59273220, Multipart: false, Headers: <Date: Fri, 28 Oct 2011 09:01:14 -0700>, <From: me@myhost.domain.com>, <To: me@domain.com>, <Message-ID: <4eaad1cab65ce_579b2e8e6c42976d@myhost.domain.com>>, <Subject: test mail gem>, <Mime-Version: 1.0>, <Content-Type: text/plain>, <Content-Transfer-Encoding: 7bit>>

mail = Mail.new
 mail.to = 'mikel@test.lindsaar.net'
 mail[:from] = 'bob@test.lindsaar.net'
 mail['subject'] = 'This is an email'
 mail.body = 'This is the body'