How do I contact a stack overflow user?
I have a question that I want to ask one member on Stack Overflow, but it seems that I can't see his email address. Is this intentionally hidden to all members?
Yes, a user's email address is private. It is displayed only to you and ♦ moderators.
You can always tell which of the items in your profile are private because they are displayed in dark red, rather than the standard black color.
So in general, there is no way to contact a specific user via email. However, some users have chosen to share their email addresses in the "about" section of their profile. Check there first, and if you don't find something, try leaving a comment to one of their recent answers.
But please bear in mind: contacting specific members is not how this site is intended to work. If you have a question, please post it for everyone to see, browse, and answer. If it is a good question, it will help other people, too. And if you post it for the entire community, other experienced users will answer your question as well, providing even more valuable insight.