Mastering Windows® SharePoint® Services 3.0

1.9. SharePoint and Email

Sharepoint integrates with email more than ever. This is why you should consider how you'll configure email when you're planning to install SharePoint.

In addition to being capable of sending alerts and notifications (which requires properly configured outgoing email), SharePoint needs to be set up to receive incoming email. This is because several lists and libraries can be enabled to receive email. The primary benefit is that you can send a new item to the list without going to the SharePoint site if you know that list's email address. And you can do of this from the comfort of your email program. No need to open a browser.

To manage incoming email, the SharePoint server needs to have the SMTP service set up locally. ...