[Mailman-Users] Unknown user when posting to a list?

Hello,

I created a list and succesfully subscribed several e-mails (the welcome e-mail was received by them). However, if someone tries to send to the list (test@thorie.com), they get an error message from the server saying that the user 'test' was not found.

Why is this?

Am I supposed to create a user account called 'test'?

Thanks in advance! --Takahiro