Hi

I'm setting up a mail server (called SERVER1) on Feisty using Postfix and Dovecot, which send and receive mail fine. On my clients I'm using Thunderbird. Basically, I want to be able to send an internal email from thunderbird just using the username of the person its going to. I can do this using webmin if i go to the postfix server mailboxes and send a message. From thunderbird it works if i type 'user@SERVER1' but it'd be better if i could just type 'user'.
Also eventually I want to have a contacts list of internal users for the network users to choose from when sending to them. How can i do this? Is it done with postfix or dovecot? or even sugarcrm, which i also use

thanks