should I be using an email service

such as:

• Amazon SES
  
  
• Postmark
  
  
• SendGrid
  
  
• SocketLabs
  
  
• MailJet
  
  
• ElasticEmail
  

The reason i ask is that I am trying to set up using smtp from optimum. BTW, I am trying to use php's send mail, not CI's mail functionality. But my application while being developed on localhost will reside on a public server (knownhost for now) so why am I using optimum? 

I am truly confused.

proof that an old dog can learn new tricks