All alumni either already have a Cornell-sponsored Gmail account or can get a Cornell-sponsored Gmail account (G Suite for Education). This service was formerly known as Cmail.

This account uses your NetID@cornell.edu address.

Some people have asked whether they can use a personal Gmail account (with an address like phil.schmertz@gmail.com) but have the messages appear to come from their Cornell address.

The short answer is no. This is known as spoofing and it's a bad thing, even if intended harmlessly. Various email systems look for evidence of spoofing and may block messages and the accounts sending them. Neither Google nor IT@Cornell support this practice.

To summarize: if you want to send email that looks like a Cornell account, send it from your Cornell account.