Sources
1 http://www.exacttarget.com/
* https://litmus.com/blog/mobile-opens-hit-51-percent-android-claims-number-3-spot
** http://blog.dotmailer.com/whats-email-worth-roi/#.VmhZMxorJTY
*** https://litmus.com/blog/a-guide-to-animated-gifs-in-email
4 https://www.campaignmonitor.com/blog/email-marketing/2009/10/lifting-your-click-through-rate-with-a-b-testing/
5 http://www.radicati.com/wp/wp-content/uploads/2015/02/Email-Statistics-Report-2015-2019-Executive-Summary.pdf
6 https://blogs.adobe.com/conversations/2015/08/email.html
