Redirecting email after you leave or graduate
If you have set up a mail alias to an external mail address CSE will maintain it for 6 months after your account expires. After 6 months it may be (silently) deleted. See Redirecting mail at CSE for details on how to create a mail alias.You could also use vacation mail to set up an auto-reply telling people you have left or graduated and can now be reached elsewhere. See Auto-replying to mail for details. Again, this is likely to be silently deleted after a few months.
What won't be deleted, for graduands, is a so-called alumni account. This is not a true account but instead is an email and website redirection service CSG offers to graduated students. Once you have created a permanent alumni name for yourself you can point it to your new email address and website URL. You can update these pointers later if they change but the alumni name doesn't change. Hence, it is a good idea to tell your friends that they can always use your alumni name to reach you.
For details on setting up an alumni account, see the alumni website.