An email subject line may say something like "From the desk of barrister [Name]", "Your assistance is needed", and so on.
The scam has been used with fax and traditional mail, and is now prevalent in online communications like emails.
The number "419" refers to the section of the Nigerian Criminal Code dealing with fraud, the charges and penalties for offenders.
In that con, businessmen were contacted by an individual allegedly trying to smuggle someone connected to a wealthy family out of a prison in Spain.
In exchange for assistance, the scammer promised to share money with the victim in exchange for a small amount of money to bribe prison guards.
One variant of the scam may date back to the 18th or 19th centuries, as a very similar letter, entitled "The Letter from Jerusalem", is seen in the memoirs of Eugène François Vidocq, a former French criminal and private investigator. One of these, sent via postal mail, was addressed to a woman's husband, and inquired about his health.
Another variant of the scam, dating back to circa 1830, appears very similar to what is passed via email today: "Sir, you will doubtlessly be astonished to be receiving a letter from a person unknown to you, who is about to ask a favour from you...", and goes on to talk of a casket containing 16,000 francs in gold and the diamonds of a late marchioness. It then asked what to do with profits from a .6 million investment, and ended with a telephone number.
Often a photograph used by a scammer is not a picture of any person involved in the scheme.
Multiple "people" involved in schemes are fictitious, and in many cases, one person controls many fictitious personas used in scams.
Other official-looking letters were sent from a writer who said he was a director of the state-owned Nigerian National Petroleum Corporation.