To show how serious you and your organization are about presenting itself as a professional entity on the Internet, it is often a good idea to have an email address associated with your website.
If someone visits your site, and they see a generic email address, they may think twice about the validity of you or your organization.
Granted, there are going to be exceptions due to specific reasons from time to time depending on the individual or organziation, but it has become the standard rule of thumb.
An example would be:
john@jd-web-designs.com
or even better yet
yourname@yourdomain.com