Email Tools
Email Testing and Preview Tools
Inbox Inspector
http://panel.inboxinspector.com
Mailtrap
https://mailtrap.io
Mailchimp
https://www.mailchimp.com
https://mailchimp.com/help/test-with-inbox-preview/
Stamp Ready
http://www.stampready.net
Spam Score Checking Tools
Mail Tester
https://www.mail-tester.com/