by definition that is spam:
2. to send an unsolicited e-mail message, often an advertisement, to many people
Google's lets you place up to 500 addresses in the To:, Cc:, and Bcc: fields combined.
Yahoo Mail limits you to 100 addressees, with a maximum of 10 in the Bcc: field
Windows Live outlook (formerly Hotmail) limits you to 100 messages per day
a good cheap solution that may give you a bit more flexibility, www.rackspace.com
although when my clients mass mail like that some times Rackspace will warn them about spamming.