We are running a mix of Exchange 2003 and Exchange 2007. Right now, I have four SMTP servers sending email to the Internet. Two 2003 and two 2007. They all have proper reverse lookups in DNS. We host our own DNS. I have been reading up on SPF records and I know we don't have any defined for our Domain. Is this something that others are doing, and what are the downfalls if any? I am guessing I just put these records on our Public DNS servers. Has anyone else done this and not had a problem with mail flow. I am concerned that I might disrupt mail flow. Are there any good articles on how to do this in a typical Exchange environment.