Snailbox - Schedule your email at specific times and recover the time you're losing to your inbox.
PixelBlock - Block email open tracking inside of Gmail
Inbox When Ready - Protect your focus... hide your Gmail inbox by default
Ugly Email for FireFox - Get back your email privacy, block email tracking
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Email Privacy Protector - Check the presence of email ids on your webpages using Email Privacy Checker tool and protect yourself from email spammers.