I will be migrating from a single server Exchange 2003 environment to an Exchange 2007 environment. Currently, the plan is for one internal server andpossibly oneEdge Transport in the DMZ. I'm trying to figure out which would be better, an Exchange Transport or a server with a third-party gateway solution such as Symantec. Right now Symantec's product looks a bit more robust. Anyone have any thoughts. What would the advantages be of using an Edge server? Thanks

Well strictly my opinion, but third party does have some advantages opposed to Edge Server. I will go even one step further and suggest Hosted Filtering as opposed to a Gateway solution. Few advantages, spam and viruses will not saturate your circuit as third party filtering will catch it before it arrives. Another great advantage of hosted filtering solution, if your WAN link or Exchange Server were to go down for any reason the filtering service will spool your mail till it comes back up. Pricing is also very competitive with Edge Transport filtering. You can trial most services such Message Labs, Postini or Spam Soap and even Microsoft Hosted Filteringfor 30 days and only requires an MX Record Change.

I totally agree with john, as I've same deployment lately, one server with 3rd part hosted anti-spam solution. It has really fasten the email send/receive as more than 5k spam is getting filtered by the hosted anti-spam, so you can imagine how much load on our internet circuit has been reduced in no time and made the email delivery faster than ever. Plus the biggest advantage is that these hosted solution run multiple anti-spam engines and a pool of IP adresses (in case if your MX get black listed). Plus it will not be your headache to manage one more appliance hope this help you.