  For selling a single item to agents with independent but non-identically
distributed values, the revenue optimal auction is complex. With respect to it,
Hartline and Roughgarden (2009) showed that the approximation factor of the
second-price auction with an anonymous reserve is between two and four. We
consider the more demanding problem of approximating the revenue of the ex ante
relaxation of the auction problem by posting an anonymous price (while supplies
last) and prove that their worst-case ratio is e. As a corollary, the
upper-bound of anonymous pricing or anonymous reserves versus the optimal
auction improves from four to $e$. We conclude that, up to an $e$ factor,
discrimination and simultaneity are unimportant for driving revenue in
single-item auctions.
