IF you are looking for free smtp server i would like to tell you that you are on wrong track :). Nothing is free and with free you cant do what you want. So you need to look for paid service but cheaper one that will not only will solve your issue or problem and will also give you nice return. Free SMTP services dont allow high volume email delivery which is do require in bulk mailing. The more emails you send the more chance of sales and traffic. So stop looking for free and start looking for cheap smtp service.

Some recommendations are

www.massmailservers.net
www.bulkmailvps.com
www.smtpvps.com
www.dailysender.com
www.hotsol.net
www.cloudsmtpservers.com
www.powermtaservers.com
www.instantbulksmtp.com