Being information security professionals, we have obligation to follow good e-mail practice, by this we can operate with due care in our profession and that will make us look good. In my earlier job, colleague of mine [a security expert] had sent me an e-mail describing how he broke the weak encryption of an application. Inadvertantly, in his e-mail, he had pasted his own encrypted password! I showed up at his office and presented this expert his own password. All I did was to follow his advice and write a trivial program to break the cipher. It is very important that we as security professionals should not  look or act stupid ;)

Check out this blog post from Marshall Goldsmith  "E-Mail Food for Thought". Excerpt from this blog:

"Managers need to worry not just about their own e-mail but also that of their employees. Email is permanent and searchable and can be forwarded as easily to a thousand people as to just one. And the results can range from embarrassing to costly to disastrous. All the goodwill you've built up over years or decades can be destroyed with one bad e-mail from anyone in your organization."