It is effectively an advance fee fraud by way of email
It is known as 419 fraud or "4-1-9" fraud after the section of the Nigerian penal code which addresses this type of fraud
The email will offer to push huge sums of money into the recipient's bank account
The recipient is often asked to go abroad to ensure the completion of the transaction
Many financial and personal details will be requested from the recipient
If you respond to the scammer the recipient will often send documents with fake stamps, forms and signatures in an attempt to deceive the recipient into thinking the whole process is genuine
The result is you will be asked for funds up front to ensure that the fake end transaction occurs
There are many other types of 419 scams, including but not limited to: offers of employment, purchases of expensive goods at reduced prices and business partnerships