How can i read a yahoo email, without the sender knowing I opened it? Any ideas? thanks

Are you using the Mail app on your Mac for accessing the account?

If so, he does not have a special program on his computer that makes the Mail app on your Mac or anyone else's Mac provide something that it does not provide or support.

Did he ever have access to your Mac?

And if a stalker, why are you opening his email to begin with? "Curiousity killed the cat."

Mark it as junk so the Mail app will send all email received from him to the account's junk mail folder.

Or change your email address.

The Mail app on a Mac is an email client that can be used to access an email account without using a browser. A free Yahoo account cannot be accessed with an email client such as with the Mail app on a Mac. A free Yahoo account can be accessed via webmail only using a browser such as with Safari on a computer. A paid Yahoo account can be accessed with an email client.

Since you are accessing your Yahoo account via webmail using a browser, I don't believe a read receipt is supported with webmail access for an email account. Definitely not supported when using the Mail app on a Mac to access an email account.

This is why I asked if he ever had access to your computer, and it sounds like he did. Doubtful you were in his presence 100% of the time when it was possible for him to have access to your computer. There may be something he installed on your Mac without your knowledge - some sort of spyware which is giving him more info than you realize, or he knows the password for your Yahoo account which lets him know when you've read his messages.

The sender does not know.

If a read receipt is requested by the sender of a mesage which requires using an email client that supports read receipts, the Mail app on a Mac does not support this.

Actually since yahoo upgraded their mail service, I get my free accounts to show up in Mail.app