Configuring IIS to advise the browser render on different IE modes
You would have already read IIS support team’s blog about configuring IIS to send an additional header to the client which would make IE to run under EmulateIE7 mode. I would also suggest you to read this MSDN article which talks about the various IE8 display modes available, and their corresponding functionality.
Here are the possible display modes and their corresponding value to be set for the “X-UA-Compatible” meta element (or for the same custom HTTP Header)
Emulate IE8 mode --> IE=EmulateIE8
Emulate IE7 mode --> IE=EmulateIE7
IE5 mode --> IE=5
IE7 mode --> IE=7
IE8 mode --> IE=8
Edge mode --> IE=Edge
Check this blog to know the syntax to add to your IIS6/IIS7 web servers. Make sure you read this MSDN article to understand the differences between the EmulateIE7 and IE7 mode – they are not just the same. There is an additional <!DOCTYPE> which will come to decide which mode to display when you use EmulateIE7 mode. This understanding is more important before you go ahead and make the changes to your web servers. So, make sure you know what you are doing!
Hope this helps!