Automatic retry on 5xx

[ewandennis]

We recommend users retry API calls that return HTTP status 5xx. It might be nice if our clients handled this out of the box.

[crobinson42]

I receive errors occasionally:

sparkPostClient.transmissions.send() 
error { SparkPostError: Service Temporarily Unavailable
  name: 'SparkPostError',
  errors: [ { message: 'Unable to contact authorization service.' } ],
  statusCode: 503 }

I'm in favor of an automatic retry.