Whack! (sound of a profound spanking)
Hmm, Im not sure about the date sorting so I would do it like this to be sure:
cat /var/mail/james/mailfile >>/root/james/oldmailfile

then copy it to your /var/mail/james/mailfile
Archive the old /var/mail/james/mailfile just be be sure before you copy it there ;)

Teabag
Sure there's more than one way, but one just needs one anyway - Teabag