I am trying to build a email messaging system for a classified site ( a la craigslist), so that users can email each other. emails of registered users are stored in a database.

What I want is for the recipients email address to be hidden from the sender's . If I just use the mail() function and dynamically get the recipients email from the database, will this email be visible to the person sending the mail ?? if the recipients email is indeed hidden from the sender's when using mail() this way, then why does craigslist anonymize's email ? isn't it already anonymous ?

Edit: so the email won't be visible to the person filling the form. SO the question remains is why does craigslist anonymizes email addresses? and whether I should implement the same ?