.send() callback called multiple times

[mathisonian]

Hi, thanks for the library!

I'm occasionally having issues with the callback to the send function multiple times. This is a problem because it breaks, for example, async.parallel().

I'm running version 0.2.5. To reproduce send an email with an unauthorized sending address, this will call the callback with error

{ status: 422,
  message: 'Sender signature not defined for From address.',
  code: 400 }

but then will also call the callback with

{ status: 404,
  message: 'Unsupported Request Method and Protocol',
  code: -1 }

[mathisonian]

Actually this may just be because of my testcase setup -- I'm raising an exception and its getting caught in the try/catch that is surrounding the callback...