mailman II

[Michael Sullivan]

OK I've gotten mailman to let me create a list (sullivanfamily) and it
sends me a notification that the list was created, but when I try to
subscribe to the list and it sends me a confirmation email that I should
reply to I reply and get the error "Error while performing operation: 
RCPT TO <sullivanfamily-request at espersunited.com> failed;
<sullivanfamily-request at espersunited.com>...User Unknown"  How do I fix
this?