"It happens very rarely that an Internet address of this calibre goes on sale," Cologne-based Sedo said. "(The) sale of sex.com offers the new owner a unique opportunity to became market leader."
Sedo, which said it is the world's biggest trading platform for domain names, is selling sex.com on behalf of US firm Escom after creditors filed for insolvency protection, a joint statement said.
Other domain names have also changed hands for huge sums in the past, with vodka.com selling for $3 million, kredit.de for €892,500 and poker.org for $1 million, Sedo said.
"Owners of domains like this have a clear competitive advantage. Visitors land automatically on the websites of the owners just by entering what they are looking for. The listing in search machines is also improved," it added.