How can I set up a local mail server on Lion? I am developing a site with django (email registration) and for testing purposes I would like to set up a local smtp server on my MBA. This has to be local because my main work location does not have an active internet connection. So does anyone know how to do this? Would I have to buy Lion Server or can I just do it through the terminal or some other program?

Any help or questions please let me know.
Lion Server isn't released as a separate OS anymore, so if you're concerned about having to upgrade your entire OS, that isn't necessary. The server programs are distributed as an add-on to a regular Lion install, for $50, through the App Store.

There are also ways to do this for free. Being somewhat unfamiliar with running email services on MacOS myself, I would probably just configure a Linux VM and run it in Parallels (or Virtualbox if you don't have it already). A quick google search also reveals that there are a bunch of other options too, such as http://cutedgesystems.com/software/MailServeForLion/