SalesHandy
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SalesHandy email tracking tool for Gmail allows you to know whether your sent emails have been read or not.
ActiveInbox for Gmail
Commercial
ActiveInbox for Gmail is an email management software for Gmail.
Gmelius
Freemium
Gmelius is a free browser extension available for Google Chrome, Mozilla Firefox and Opera that customizes the look and feel.
Compare Boomerang with alternatives
Compare SalesHandy and Boomerang and decide which is most suitable for you.
Compare ActiveInbox for Gmail and Boomerang and decide which is most suitable for you.