The first step in cleaning your list is to trap bounced messages in a central location.  We suggest that you create a "bounce box".  A bounce box is a dedicated e-mail account that is setup to trap returned messages i.e. bounce@yourdomain.com.  To be sure that returned messages find their way to your bounce box you must understand how these messages are routed by SMTP servers. 

When a message is submitted to an SMTP server it is tagged with a reverse-path.  The reverse-path is specified by the sending application with the MAIL FROM: command as outlined in the SMTP RFC-821.  The reverse-path is the path the the server should use to communicate with the original sender of the message, and therefore the reverse-path is typically the e-mail address of the sender (the from address). 

The SMTP sever stores the reverse-path internally, not in the actual message, and forwards it with the message through any relay servers as necessary until the message encounters an error or reaches its destination. Since the return-path is not recorded in the actual message it is typical to add a From: header to the e-mail message which contains the address of the sender and an optional friendly name. i.e. "Joe Sender" <joe.sender@domain.com>.  Mail readers use the From: header to display who a message is from.

It is very important to understand that the reverse-path and the address in the From: header need not be the same.  Therefore it is possible to send a message which will be displayed by mail readers as coming from joe.sender@domain.com, but has a reverse-path of some_other_address@domain.com. 

Once you understand the difference between the reverse-path and the From: header, and the roles they play, you are on your way to building messages that will be displayed in a friendly manner if delivered, or will be returned to your centralized bounce box if there is a failure.