I installed Plone 4.0.7 on Windows Server 2008 64bit, and tried to add a new user. However, when I checked "Send a confirmation mail with a link to set the password", the new user was not created. Otherwise, I could create a new user. When I tested my mail setting on Windows 7, there was no problem. I could create a new user and send a confirmation email. I also opened the TCP ports (25 and 587) on the firewall of Windows Server 2008.
Does Plone have a compatibility issue with Windows Server 2008 64bit?