If you've already left SU, you needs to change your forwarding at the alias level. You can redirect your email alias via https://netid.syr.edu/selfserv/home.
Please refer to Resignation or Retirement: what happens to Exchange?
1) Log into your email via exchange.syr.edu.
2) Select the gear icon in upper right corner, and then select Options.
3) Under the Mail tab, click on 'Inbox and sweep rules', then click on the plus sign.
4) Insert an appropriate rule name in the Name box. Select "Apply to all messages" under "When the message arrives...". Select "Forward the message to..." under "Do all of the following" and then enter the email address to forward it to.