To have mail sent to a POP3 account and also have it forwarded off the server, open the email admin console and:
1. Create the POP3 account
2. Create an alias with the same name as the POP3 account
3. Edit the alias and add the 2nd forwarding address to it
Mail will be delivered first to the Alias, which in turn will "see" a
local POP3 account and a Forward. The Alias will then deliver the
message to both the local account and to the remote forwarding address.
This can also be accomplished through a "routing" change. See appropriate article on "Email Routing".