Re: Devils advocate.
If the acts described in the email were illegal or likely to damage the company (industrial spying, for instance) forward it to the boss. If not, delete or forward, then forget about it. Such breast-beating over a trivial faux pas. Now, if one of the parties involved was the spouse of the original poster, I would understand the agita. Otherwise, you caught a co-worker doing something embarrassing, like dancing to music in their office or picking their nose.