GlockApps - G-Lock Apps is an interesting tool that might seem simple to some, but is quite essential to most online marketers.
dmarcian - Safeguard your email from abuse
Proofpoint - Proofpoint provides cloud-based email security, e-discovery and compliance solutions for companies to protect sensitive business data.
Vetter - An online suggestion box for employees
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.
Litmus - litmus tests and tracks your email campaigns, so you can always put your best design forward.