less than 500k talking to the box?

>    I've got a netBSD 1.5.2 runing in an old HP Vectra which I use
as a
>    router (NAT + PPP + 2 Network Interfaces).  The problem is
that
>    there is a client with W2K that wanna send a big email[500k] via
>    POP3 protocol & when it does Internet Connection Freezes for
>    everything so PPP must be restarted to come back to sanity,
but if u
>    try again the history repeats. so.......
> Can Anybody help me ?
>        Samiel