How can I tell if an email I have sent has been opened?

[AT]

As per subject.

 

[Vince Averello [MVP-Outlook]]

You can try using a Read Receipt but many users block the return of them

 

[finchum]

you pay for it:

http://www.readnotify.com/

you can try it out for a short time...then you pay...but it's pretty
much guaranteed to get you the results you want...

 

[Alan]

As per subject.

Request a read receipt.

But-
it annoys most people,
most people don't send the receipt
You may get blocked by the recipients for annoying them.

People can still read your mail and cancel sending of the receipt.