Before sending email to another member, you should check their profile address to make sure it's not "cloaked." Some people intentionally obscure their email addresses to escape the notice of spam robots, which constantly scan the web looking for fresh victims. Look for these signs of a cloaked address:
Note that this list isn't exhaustive - if it were, the spammers would just program their robots with everything on the list, defeating the entire purpose! The idea is that everyone does something a little different, choosing a scheme that's self-explanatory to real humans, but inscrutable to robots. So use your real-human common sense, and look at each address to see if it looks like it's cloaked in some way.