how to know that a E-mail has been read

49experience wrote:

Sure thanks, but when I want to quit my job, or end a subscription by mail, it will help that the mail has been read

There is no way to do that. Even a "read receipt" if the recipient chooses to allow it, will not tell you that it has been "read."

For email, the "read receipt" only states that their email provider sent the message to the recipient's inbox.

Even on an Exchange server where it does indicate that the message was opened, it doesn't mean it has been read.

If you want to quit your job, you should talk directly to your supervisor. If you sent me an "I Quit" email, you certainly wouldn't get any sort of positive recommendation.

Ending a subscription is not read by anybody. The listserv just processes the subject line for "unsubscribe."

The only way to know is if the recipient tells you.

It is none of your business if/when I read my email unless I do as suggested by dialabrain.