The most common example of a scam letter is a phishing scam. These scams are designed to steal information from an unsuspecting person by posing as a familiar entity through mail and email.
A scam letter claiming to be from PayPal is one of the most common phishing scams conducted by email. This is because PayPal is very familiar to most people who shop online, so the scammer has good chance of reaching someone who uses PayPal. The letter will claim that a user's account has been deleted and that they must click a link in the email to recover their account. This link will lead the user to a third-party site disguised to look like PayPal. The user will then mistakenly input their PayPal email address and password, which the scam website will store.
PayPal will never ask a user to provide their account information in an email. This scam can be detected by checking the email address of the sender, which will likely not look like a PayPal email address. There will also typically be misspellings and other clues contained throughout the message. Another common trait of this scam is a threat contained within the body of the email that will urge the user to act quickly to avoid some consequence, such as their account being permanently deleted.