One of the many ways that scammers try and steal your information is through what is called a phishing email. It is an email disguised to look like it's from a legitimate source and attempts to gather information from you. 
I've attached an example below, this one is not as clever a some that are out there. I've circled and numbered some of the things to watch out for.
- Claimes to be from USPS but the email address is not accurate. 
 - Be especially wary of emails claiming to be from any government agency. These emails will try to use your fear to get what they want. 
 - actual emails from government agencies will end in .gov and contain the agency acronym after the @ symbol. (example: donotreply@ereceipt.usps.gov)
 
- Generic introduction with no reference to a name or tracking number.
 - Still no identifying information. 
 - a tracking/ticket/case/account number is missing leaving the potential victim unable to verify the information on the relevant company's actual website.
 
- A request for more information with a link that doesn't show where it is trying to send you.
 - An address not in any way related to the company the email is supposedly from.
 
Example of Phishing email