[O] #+EMAIL:... does not produce email by org-export-as-html

[ishi soichi]

emacs23.2
org7.4
MacOSX SnowLeopard

I put

#+EMAIL: soujiro0...@gmail.com

 in an org file, hoping that org-export-as-html will produce <a
href="mailto:...";></a> in the resultant html file.
But it does not.

I have not idea why.  Do I need some other options or whatever?

soichi