What do you mean, trace an email/trace a signal?
If you mean get a message or data from when a user reads an email you send, you can only do that by attaching a program to the email, usually a virus. This is illegal (sending viruses.)
If you are using corporate email (email inside an organization, some software (like Microsoft Outlook) allow email receipts. This only tell you if the email was read or not. No more info. As far as I know, this only works in corporate environments.