A San Francisco-based startup called Streak has developed a free Google Chrome browser extension that’s changing the email game: the extension lets email senders see when recipients open an email.
Using your gmail account and this installed tool, you can tell when people open your emails. Using the utility, an eye icon will appear when the user has read the email. Users on the other end do not have to have the extension installed for the feature to work.
This could be very handy when sending proposals, estimates, invoices or other such things.