With Google Apps Mail's "Mail Fetcher" you can set-up your inbox to receive email from multiple accounts (e.g. a personal Gmail account, a school alumni account, etc.) Mail Fetcher can download messages from up to five other email accounts, centralizing all your email in Apps Mail.
Setting up Mail Fetcher is easy and free, but the email accounts you'd like to fetch from must support POP access and, in the case of Gmail addresses, have POP access enabled. Some free email services don't offer POP access to their users, so please contact the customer service department of your other webmail provider to determine if POP access is available in your non-Google email account.
Once you've set up Mail Fetcher, Google will check your other accounts on a regular basis, and new mail will appear automatically in Apps Mail. Google Apps Mail checks individual accounts for new messages at different rates, depending on previous mail fetch attempts. At this time you can't customize the frequency of automatic mail fetches.
Not only can you receive the email from different accounts, but you can send mail as well. So if you're receiving an email from a personal account into your school's Google Apps mail account, your reply will be from your personal account, even though you sent it while in your Google Apps inbox!