not sure what your situation is, your description is too vague
so let's say this guy has an email address annoysome@yourCompany.com, then he has two other email address such as user@gmail.com, and user@163.com?
if this is the case you don't have to put gmail.com and 163.com into his AD account, that will just do nothing. You dont have to setup pop3 virtual server either, that is useless in this situation either. It's only something you need to config in Outlook profile so it points to gmail and 163's pop3 server respectively.
so let's say this guy has an email address annoysome@yourCompany.com, then he has two other email address such as user@gmail.com, and user@163.com?
if this is the case you don't have to put gmail.com and 163.com into his AD account, that will just do nothing. You dont have to setup pop3 virtual server either, that is useless in this situation either. It's only something you need to config in Outlook profile so it points to gmail and 163's pop3 server respectively.