SharePoint 2007 allows for emails to be accepted into discussions, document libraries and lists. To enable this functionality, a few steps will need to be followed. One thing to note: integrating SharePoint with Exchange is NOT needed for this functionality, but if you do choose Exchange, you will get some added benefits.
-SMTP Service
You will need to install the SMTP Server Service on the SharePoint server. This is done via add/remove programs, and within the IIS component listing.
-Enable Incoming Email
Now, enable Incoming Email from the Central Administration website. It is found by following: Central Administration > Operations > Incoming Email Settings
-SMTP Connector
You will finally need to configure an SMTP connector within your email server so it knows where to send emails you designate for SharePoint.