Email addresses for root

[sadsjon <jon.rowlan@sads.com>]

I have been wondering for some time how Debian identifies a mail
address for the root user and indeed any local users.

I have recently cloned my server, changed hostname all correctly but
any mail sent from root using mutt comes in as if from the previous
server name and not the new one.

I would like to know how to change this.

I would also like to have local server "root" mail send to an external
postmaster account and have never been able to do this either.

I am using sendmail/spamassassin/mimedefang/clamav/lenny/squirrelmail/
courierimap

my /etc/aliases file contains no mail addresses, just single word
usernames.

Can anyone tell me where these are held and how to have my root mail
sent to an external postmaster mail address please?

Many thanks,

jON