Is there a program that will tell you if someone opens an email? Is that legal or an invasion of privacy?

Outlook and some other "Mail Clients" can flag an e-mail message so that a return message is generated when the mail is downloaded and another when it is opened. If you delete e-mails unread when they are still on the server (using webmail) that does not generate a message.

Don't allow an automatic message as hackers can use this facility to invade your computer. Find the "Options" menu and untick the "automatically send mail receipts" box. You will then be prompted each time you open an e-mailand you can choose to send the reply or not.

Lots of email programs let you request a return receipt for emails. Its up to the person receiving the email whether to send one back or not. If you dont want to send one just click no when asked if you want to send a return receipt. I havent heard of any programs that do this but it may exist. Hope I helped you at least a little!

It's only possible on private mail systems. It's not possible on Internet mail. They can ask you to send a read receipt, but most Internet mail programs and systems simply ignore it.