[Dovecot] Backing Up

[Neil]

What is the best way to do a (server-side) backup of all mail in a  
user's mail?

I don't think I'm doing anything weird as far as configs go; here's  
dovecot -n if it helps:

# 1.1.4: /etc/dovecot/dovecot.conf
protocols: imaps
listen: *, [::]
ssl_cert_file: /etc/ssl/dovecot/cert.pem
ssl_key_file: /etc/ssl/dovecot/key.pem
login_dir: /var/run/dovecot/login
login_executable: /usr/libexec/dovecot/imap-login
mail_location: maildir:~/.maildir
auth default:
   mechanisms: plain login
   passdb:
     driver: pam
     args: *
   userdb:
     driver: passwd
   socket:
     type: listen
     client:
       path: /var/spool/postfix/private/auth
       mode: 432
       user: postfix
       group: postfix