MOSS 'Exires' Header

Dear Microsoft,

What is an "Exires" header? I know what an "ExPires" header is but I have a feeling none of us (not even IE) know what to do with Exires.

Sometimes you've really got to wonder whether MOSS went through any form of QA whatsoever (and our system administrator often asks that exact question). Below is a set of typical HTTP response headers for a file requested from MOSS.

HTTP/1.1 200 OKConnection: Keep-Alive
Content-Length: 453
Date: Mon, 05 May 2008 04:44:34 GMT
Content-Type: image/gif
ETag: "{E4BBF3CA-94E3-44CB-A5CF-DD38E3330E11},3"
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 12.0.0.6219
Last-Modified: Wed, 19 Dec 2007 05:52:22 GMT
ResourceTag: rt:E4BBF3CA-94E3-44CB-A5CF-DD38E3330E11@00000000003
Exires: Sun, 20 Apr 2008 04:44:34 GMT
Cache-Control: private,max-age=0
Public-Extension: http://schemas.microsoft.com/repl-2

Note the useless Exires header. Without the extra 'p' this header is going to float right through any caches and will be ignored by the user agent. Not only that, but Exires is pumped out with most MOSS-based resource--that is any resource delivered from the MOSS content database (images, CSS, etc) excluding pages. Due to their size, images are great candidates for caching; likewise for the number of smaller files, like CSS and JavaScript, that otherwise clog up your page load times.