Custom “.html” permalinks

Hi,

I’m trying to create custom permalinks using the following format:
/%postname%.html

It doesn’t seem to work though. I just end up with permalinks using %postname%. I got this working once on a previous version of WordPress by hand working the .htaccess file, but it looks like WP now handles permalinks internally.

I’m using WP as a CMS for an old site, so I need to be able to keep the urls consistent (so I don’t lose search engine placement).

Thanks for your help!