I like to put a line along top edge of page "Interested in acquiring or advertising on ***.com, please contact us." The "contact us" is a link to that website's contact page. Emails arrive at my central hub email address telling me which website sent the message and referrer information is attached to the message so I can see how the person arrived at that domain. Each hub has a few hundred such websites, contact form protected with captcha, overall efficient and avoids posting an email address that will be spammed.