If you are looking for cheap smtp servers for email marketing that can give you good results and allow you to send unlimited emails to unlimited subscribers at affordable price with IP rotation, rDNS, SPF, DKIM, DMARC setup in free I would recommend you to see the bellow few links they may be helpful for you.
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