I've confirmed that the SendAcceptEncodingHeader metabase setting that USED to work pre ISA (Internet Security and Acceleration Server) SP2 and allowed IIS to pass through the compression headers for gzip, is no longer working with SP2 (and passed this on to Microsoft).
The other option, is to of course use ISA SP2's spiffy new (and highly touted) compression. So I turned it on to give a run. It ran fine...for about 20 minutes. Then it crashed with an error of : "ISA Server was unable to decompress a response body from /RentACoder because the following error occurred: 0x80070008." I tried turning off the decompression (unchecked the checkbox on the 3rd tab)...and still got the same crash after about 30 minutes.
So I brought this up to Microsoft support, and the engineer passed on that Jim (the ISA manager) said that the compression features were designed for branch offices. Nice to know about that qualifier in advance, huh? :)
Unfortuantely I'm stuck between a rock and hard place with SP2. I installed it becuase Microsoft reworked their handling of large attachments, and they felt it would fix the ISA crashes I was having every 1-4 weeks. And it looks like it is doing the trick (no crash for 3.5 weeks now). But now my bandwidth costs are going to be 2x-4x higher this month than they should be due to ISA SP2's new "feature". I can't win either way. (The Microsoft tech I'm dealing with, Masoud, said he'll try to get duplicate this and get something going in a week or so...I hope he can pull it off).
However, it could be worse. I've done some reading on newsgroups and Microsoft is slammed with other problems in this SP2 concerning compression in the opposite direction...people browsing from behind ISA SP2 seem to have problems. Thankfully that isn't my situation too.
Ian Ippolito
http://www.RentACoder.com
4/27/2006: UPDATE: There is a workaround to fix this problem. If you completely disable the new and "improved compression .dll that SP2 has so generously forced upon you (but that doesn't work)...the compression metabase setting works again! To do this:
Go to "configuration", "add-in", "web filters" tab. Then disable "compression filter". Viola...enjoy!
Ian Ippolito