I just found out that Peter Vogel included smtp4dev in the above article in Visual Studio Magazine "17 Free Tools for Visual Studio". Unfortunately his feedback isn't totally positive because he had some problems with the message inspector window crashing (thought that was fixed in an early 2.0 version?). A subsequent letter from a reader recommended PaperCut... 

I'm sorry that Peter had problems. Unfortunately he didn't provide any detail about the problems he had, so I'm still none the wiser. Nobody has logged this problem on the issue tracker either. Anyway, I'll get to the point... If you are having problems with smtp4dev, please please please tell me about them and if possible provide details on the issue tracker. That way I can actually resolve them rather than just speculate what's going on. For most bugs people have emailed me about or put into the issue tracker, where I could reproduce them, I've been able to provide a release containing the fix within a few days.