Change Functional Level 2003 to 2008

Hi,

Need Help

Our environment is currently in Windows 2008 R2 Server. All AD is using Windows 2008.

But we still have Ms Exchange 2003 on Windows 2003 Server

We plan to change our AD functional level from 2003 to Windows 2008 R2.

Is there any impact to our Exchange if we changed AD functional level?

Thank you.
Venmii