limiting pop access to gmail servers ?

[George Sanders]

We run our own (freebsd) mail server.  It's a pretty classic, old fashioned 
/var/mail/username setup.

We have enabled POP so that certain people can pop their mail from us, and use 
gmail as their mail client.

However, we have no other POP users ... and I don't want POP open to the whole 
world ...

BUT, I suspect there are a LOT of possible IPs that google will use to pop mail 
from us ...

Is there an authoritative list ?

Anyone else blocking POP access to everyone BUT google ?