The million dollar question , why can’t you use yahoomail or gmail or any other
free mail server ? Do you need a dedicated Email server?

Every one of the free mail servers out there puts a limit on how many emails you can send at a time. Some limit you to a few hundred per hours, while others won’t allow you to email more than 25 addresses at once.
With these types of limits, you won’t be able to market the way you need. Sometimes you want to be able to send out thousands of emails in a short amount of time. Without your own server for email marketing, this simply isn’t possible.

All communication needs are met by using this server

Webmail - It would give you full access to any web browser. It also has a very instinctive and user friendly interface
Instant messaging - No matter how many emails you have