Can I use mod_deflate to compress files on the fly?
We have the Apache mod_deflate module available on our servers, and it can be set to compress data requested from your site.
What if I'm using WordPress?
The WP Super Cache plugin we recommend can compress cached files when they're created. This speeds things up even more: in most cases, the HTML pages will already be compressed, and mod_deflate won't have to do any work at all.
So if you're using WP Super Cache, you should enable the Compress pages so they're served more quickly to visitors feature (in addition to following the above instructions if necessary). That gives you the best of both worlds.
How can I tell it’s working?
The third-party test site “Check GZIP compression” can confirm that your site is sending compressed files.