Our OTRS 3 server is hosted on an Amazon EC2 Micro EBS Instance with an assigned Elastic IP.
The monthly cost for the instance is less than $18 and handles our ticket volume very well.

Our regular email is serviced by Google Apps for Business (premium edition) where the addresses are
emailaddy@ourdomain.com

We use a Google Apps free edition domain for service accounts including the main OTRS mailbox which is 

helpdesk@ourdomain.net

This is the primary address which OTRS uses, polling the mailbox every two minutes using the OTRS fetch mail cronjob

Google Apps allows up to 30 alias email addresses per individual.  We have aliases set up that correspond to queue names, e.g.
desktops@ourdomain.net >> desktops queue
servers@ourdomain.net >> servers queue
malware@ourdomain.net >> malware queue

Even though all the messages go to the same helpdesk@ourdomain.net mailbox OTRS can see the to: field of each message and routes the messages accordingly.  I should think that this same method would work for technician emails as well, even though we're not using that method.  In this way each of your technicians could have a proper email box in the primary company domain for regular internal correspondence, and a helpdesk email address in the service domain to give to customers to keep those emails on the helpdesk.

Rob