In short, nothing. Norton AntiVirus's e-mail protection function will not work with a GUMail account.
POP accounts download e-mails from a server to the client's computer.
GUMail is an IMAP account, and Norton AntiVirus's e-mail protection only works with POP accounts. This is nothing to worry about. Configured properly , Norton AntiVirus will provide you with all the protection you need.