PIX locking up SMTPLocked
We have a Cisco 520 PIX firewall, runing IOS 6.2, between our router on the internet and our internal network. The internal network is a Windows 2003 network with Exchange 2003 mail server. 3 times in the past 2 months the SMTP traffic to and from the outside world stopped. The Exchange Server should no events in its logs and was handling internal traffic just fine. The only sign of trouble was a lack of inbound messages and a growing outbound queue. VPN traffic was passing through the PIX as was Web Browsing traffic. In each incident, the only way I could restore the SMTP traffic was to reboot the PIX. Does anyone have any suggestions as to what might be causing this problem and how to remedy it?