Setting the email object’s BounceAddress property controls where mail bounces will be delivered. To help in testing, Chilkat has setup a mailbox, firstname.lastname@example.org, that you may use for testing. It is a mailbox that is already full (intentionally), and any email sent to it will generate an automated "mailbox full" bounce reply.
Here is an example program in C#:
C# Bounce Testing Example
(The identical example is also available in other programming languages at example-code.com.)