MockSmtp 1.5.1 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. This application's bundle is identified as com.xilinus.MockSmtp. The latest version of MockSmtp can be downloaded for Mac OS X 10.6.6 or later. The MockSmtp installer is commonly called setup.zip. The most popular versions of the program are 1.5 and 1.2. This Mac application was originally created by Xilinus. MockSmtp for Mac lies within Developer Tools, more precisely Webmaster Tools.
From the developer:
MockSMTP is a native Mac application that embeds its own SMTP server. It also features an e-mail client browser, enabling instant viewing of both raw content and HTML rendering, so you can see how your mail looks when delivered. Configuration couldn't be simpler: just run the application and everything's set up. You don't even need an Internet connection for it to work!
You may want to check out more software for Mac, such as ModelBaker, iGooMap or PageRank Viewer, which might be similar to MockSmtp.