There is more than one way to obtain students' e-mail addresses.

Use PeopleSoft's Notify Listed Students" Feature to notify Students by E-Mail

With this feature, you can Select some or all students in the Class Roster and send an e-mail from within PeopleSoft, or you can copy/paste the e-mail addresses into an e-mail program.
 

Run a Report to get a list of Students

With this feature, you can follow the steps to run a "Student E-Mail and Phone Report" that results in an Excel sheet or PDF that lists Student ID, Name, Phone and E-Mail. 

NEW Fall 2011: Use the new E-Mail Column in the Class Roster

There has been a column with students' e-mail addresses added to the Class Roster ("little people" icon, not the "Web Class Roster" button).