TestSubject - Test how your email subject line displays on mobile devices.
Hunter - Find all the email addresses related to a domain
analyze.email - Test the spam-y-ness of your emails
Snov.io - More leads. More sales. More revenue.
Rename Email - Easily change the subject of any email, by cloudHQ
Apollo.io - Apollo’s predictive prospecting, sales engagement, and actionable analytics help the teams to reach its full revenue potential.