I needed to send mail for a user control I was writing and since the move to Windows 7, I hadn't yet figured out what to do about W7's lack of a SMTP server.
Here are two solutions that I found and I'm kind of on the fence about:
The first is a full blown local SMTP server called, Free SMTP Server and I've used it in the past. Not much to say here. It just works.
The second, smtp4dev, is interesting in that it doesn't actually send email messages. This is great, for when you are just testing the format of a message and would typically go through multiple revisions that you'd then have to delete. Sure, it's a minor irritation to find those emails peppered among your other daily messages, but another benefit is that smtp4dev sits in your system tray and can be configured to display the "email" as soon as it is received instead of you having to browse to your email client and open the message. My only wish is that there could be a "we'll do it live" switch that would actually send the email for those cases when your email needs to be processed by another system. I don't like the idea of installing two SMTP servers.