[Mailman-Users] Delivery error to virtual list

[MP Netsai]

Can someone please point me in the right direction. I have just recently 
built Mailman for virtual domains. I have followed the guidelines on section 
6.2.12 (Virtual Domains) {http://www.list.org/mailman-install/node28.html}. 
I am using Exim 4.80 and Mailman 2.1.14 on a FreeBSD 9.1. The error on 
trying to deliver message to a created list comes back as "unknown user", 
eg.

exim -bt createdlist at mydomain.com
createdlist at mydomain.com is undeliverable: Unknown user

I am not sure if my error is on my transport or router configuration. Would 
very much appreciate some help.

Many thanks,

Netsai.