Since installing our new network infrastructure, we use ISA server with exchange running on its own server. We used smtp vs on the ISA server as recommended in the book (the same one as on this site). We installed everything according to the book. External emails and then got delivered. But this only happens for some random time and then stops. We also use the VPN option to connect a remote option, which by the way works 100%. Now the only way we could get external mail to come in again was to restart the ISA server. Mail then got delivered for some time (normally about 1-2 hours) then stoped. We then removed the local smtp vs on the ISA server. Thus no content checking is taking place (we use an external lab to check content and viruses anyway) and smtp packets get forwarded straight to the exchange server. Now it has been working for 2 days, fingers crossed!!! Any ideas why this happend?