If you have bought Windows Small Business Server, then you will have Exchange, which is Microsoft's Email server. Linux also has it's own Email server which you can use.
People often want to have their own email system without realising the problems with this. The biggest problem is backups. You need to use backup software that is capable of backing up your email system and you need to be 100% sure that the backups are working.
As a general rule, if you have less than 10 people and unless you need calendaring, then you are better off sticking with POP3 with your ISP. Once you have more than 10 people, then the convenience of being able to make your own changes to your email system generally overrides the simplicity of using your ISP.
Be aware that POP3 isn't overly secure. For 99% of businesses, this is fine, but if you require high security, then you need to look at encryption and using your own email system.
Small Business Server provides a wizard that helps you configure your Email and Internet connection. Generally you can get this to work first time and setup the email system yourself.
We can't overstress the importance of knowing what you are doing if you have your own email system. Microsoft Exchange in particular, is very fussy about how it is backed up and restored. If you don't get this right, you may lose all of your emails.
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