Silent Read Confirmation
I would love to have an email client that tells me whether the recipient has opened the email. Gmail plug-ins like 'Streak' have this. Ideally the read receipt happens silently without the recipient having to approve another outgoing mail back to the sender.
Rene A Sierra commented
Feature is unreliable. Please improve
Blackberry has this for years and new email app Spark. Great option to stand out from all the other email apps.