Faced those times when you sent an important email to someone and later they told you that the email wasnt received ? This service can help you.
Spypig is an email tracking service that will send you a notification when your recipeint receives your email. It works with most popular email services like Gmail, Yahoo and email clients like Outlook and Thunderbird.
The service is free and very simple to use. Just enter your email address and the subject of the email you wish to send. Then choose a tracking image and the number of times you wish to be notified about the recipient opening your email. On activation, it should show you an image, right click the image and paste it into the email you wish to send.
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The problem is that regarding email one just can talk of “seen” email, this is, mail opened in the client. You can’t tell if an email has truly been “read” or not.
Moreover I don’t think it fits into “netiquette” sending this kind of confirmation.
Very less free service like this right now. Maybe can have a try with whoreadme.com, readnotify too.