From https://en.wikipedia.org/wiki/History_of_Gmail#Extended_beta... :
> During the early months of the initial beta phase, Gmail's well-publicized feature set and the exclusive nature of the accounts caused the aftermarket price of Gmail invitations to skyrocket. According to PC World magazine, Gmail invitations were selling on eBay for as much as US$150, with some specific accounts being sold for several thousand dollars. After a new round of invitations in early June, the price for invitations fell down to between US$2–$5. Websites such as Gmail Swap emerged to allow philanthropic Gmail users to donate invitations to people who wanted them. On 28 June 2004, Google amended its policy to forbid the selling of registered accounts.