Email types

[moiseevigor]

http://support.postmarkapp.com/customer/portal/articles/64742-what-are-bounces-and-spam-complaints-

List of messages: https://github.com/mailgun/flanker/tree/master/tests/fixtures/messages

[moiseevigor]

Constants in class: http://stackoverflow.com/questions/8750724/what-do-you-use-instead-of-enum-in-doctrine2