Why you need dedicated email server hosting?
If you are mass mail sender or you want to send 1 million emails per day or more. Then google smtp, smtp server hotmail, aol mail server, yahoo email server and free smtp hosting server won't work for you.
Because Gmail, aol, hotmail, yahoo and all free smtp server providers do not allow to relay unlimited emails per day or per hour from their email servers. They apply limits on outgoing emails which will slow down your email campaigns and you will lose the opportunity.