While emails are free to send, there are still costs involved which can become substantial as the volume increases. The bandwidth they travel over, the storage space they take up, and the connectivity used to download them to the end-user are all services with costs associated. None of these costs are paid by the spammers, but rather by the people they reach and the email providers whose servers are used.

Since emails are easily and cheaply sent, their use in advertising quickly got out of hand and a number of measures are needed to keep this abuse under control.