10 Types of Subject Lines
http://discover-your-customers.com/10-headline-types-to-help-you-attract-the-right-audience/
15 Tips For Writing An Excellent Email Subject Line
http://www.businessinsider.com/how-to-write-an-excellent-email-subject-line-2014-3
12 Types of Email Subject Lines That Will Increase Your Open Rates
https://www.instapage.com/blog/email-subject-lines
380 High Emotion Persuasive Words
https://www.thepersuasionrevolution.com/380-high-emotion-persuasive-words/
400+ Words That Trigger Emotional Responses
Other References
Email Subject Line "Spam" Trigger Words
http://theidsp.net/blog/bob-the-builder-blog-5/post/74-subject-line-spam-trigger-words-37
Headline Templates
http://theidsp.net/blog/bob-the-builder-blog-5/post/headline-templates-