I have OTRS 2.4.7 installed, and want to use sendmail as i don't want to
use up a pop 3 license for each of the email queues we will need.

So, sendmail has been setup for to allow relaying to/from our mailservers 

I can email the otrsuser@ourotrs.ourdomain server and the ticket will go
into the raw queue.

I have created another queue and an email address for
tech@ourotrs.ourdomain and attempted to get an email to that, but keep
getting 550 5.1.1 user unknown. 
Adding the user in virtuser table in sendmail does not help as the error
remains, but creating a system user stops the error - however i recieve no
email then. I assume that it goes into /var/spool/mail/tech

Coud anyone help with this please?