Properly handle the reply_to header value

[MickaelBergem]

See #34 and #50 for the details.

[andriisoldatenko]

@MickaelBergem Thanks for creating patch. Can you please add unit tests?

[kevin-brown]

So, the Reply-To header supports setting multiple addresses, and Django handles this by making reply_to a tuple. SendGrid actually supports multiple Reply-To addresses as well if you set the header.

http://stackoverflow.com/q/15820418/359284

Unfortunately it looks like the web API does not handle multiple Reply-To addresses. I'm not sure if you know of a good way to get around this, or if it should just be documented that the SendGrid plugin doesn't support multiple addresses.

[vinitkumar]

@MickaelBergem does your patch work?

[jancsarc]

It isn't working for me so far...

[MickaelBergem]

@vinitkumar @jancsarc sorry guys I lacked time on this and never provided the unit tests, and gave up using my fork, don't remember if I was able to use it successfully.

Feel free to test / post the error you are getting here / take over the fixing of this bug :)