@bakura10 Mailgun is confusing because you can send the message via `curl -F` as separated form fields, described [here](http://documentation.mailgun.com/quickstart.html#sending-messages).  On the other hand, the [API docs state](http://documentation.mailgun.com/api-sending.html#sending) "You can use commas to separate multiple recipients.".

We're now using the 2nd method (comma separated), I guess the array will work too, but for this PR it's better to keep it consistent (so @Nikolajpetersen please use the `implode` here). If the comma notation does not work, we could have a bugfix PR @Nikolajpetersen which addresses that (but we should at least confirm first that the comma separated strings don't work anymore).