In the JavaMail API -which is what you'd use to send emails from Java- you'll see that the Message class has addRecipient methods that let you add multiple email addresses at the same time, so what you're asking can be done.
However, putting all recipients in the To field is considered very bad practice - it exposes all addresses to everybody, which has consequences both concerning security and privacy. You really should not do that. It's much better to program a loop and send those emails individually. [ January 22, 2008: Message edited by: Ulf Dittmer ]
Putting all recipients into the BCC field would solve the privacy problems. But there are other advantages to sending one e-mail per recipient. For example, if there was a badly-formed address in your list, your server might not send messages to all of the other well-formed addresses. You would have to do some testing and fiddling about to make sure you knew how that would work and how it could be made reliable.