If it worked before and the mail stays in the mailbox than there is simply no forwarding done. Assuming you have tried:
sudo service postfix restart
Have you tried checking if your forwarding adress is still correct in:
sudo vi /etc/postfix/virtual
If this checks out te be ok you could also redo:
sudo postmap /etc/postfix/virtual
If this still does not work than you could post your /etc/postfix/main.cf (minus personal information) and the /var/log/mail.info log of your last email attempt.
These last two files show very valuable information for solving problems in postfix.