Mail::Bulkmail::DummyServer is a dummy class for dummy server objects.
Mail::Bulkmail::DummyServer is a drop in replacement for Mail::Bulkmail::Server.
Sometimes you just want to test things on your end - make sure your list iterates properly, make sure your mail merge is functioning fine, make sure your logging functions are correct, whatever. And in those cases, you probably don't want to worry about futzing around with your SMTP relay and sending junk messages through it that you don't care about. Not to mention the fact that those probably will need to be inspected and deleted later. A hassle for debugging.
Enter DummyServer. This is a subclass of Mail::Bulkmail::Server that behaves exactly the same except for the fact that it doesn't actually connect to a server. Instead, it sends all data that would be going to the server to a file instead. This file should be specified in the conf file.
#in your conf file
define package Mail::Bulkmail::DummyServer
dummy_file = ./my.dummy.file
Now, instead of sending commands to your SMTP relay, they'll get sent to ./my.dummy.file for easy inspection at a later date.