On occasion, I’ve been asked “How can I tell if someone has read (or even received) my email?” Unfortunately, you probably can’t.
From a practical matter, you won’t be able to tell unless you are talking about a corporate network which the IT guys have set up to show receipts — and, even then, you will only be able to tell for emails that are completely within that installation.
Although many email programs have the ability to request a “receipt,” unless the receiver’s email program is (1) capable of sending a receipt, and (2) the receiver has it set to send a receipt and (3) no other configuration acts to block the receipt, then you won’t get it.
In my case, Eudora asks me before it generates a “receipt.” Then, because of the way I have my email configured, even if I wanted it to send a receipt, it will fail, because I have not set up the “persona” that receives the email to be able to send an email — which is good, since I don’t want to send receipts anyway.
On the other hand, if you use HTML email, a link to load a graphic can be used as a “receipt.” Many spam emails include a link to automatically download a 1-pixel transparent image. Since it is tiny (only one dot) and transparent, you never realize that your email program pulled in that image. The spammer’s server keeps track of which links were used to get images. The link always has a _unique_ code, so the spammer can tell which emails (and therefore email addresses) were actually viewed (or “previewed” in the Outlook or Outlook Express preview pane). [Why do they want to know? Because they can resell a “confirmed address” (one where they know there is someone who might read the spam email) for a higher price than an unconfirmed one.]
However, for you and me, no, we don’t have an easy way to know for certain whether someone has read, or even received, an email we sent.