We have a new 5520 in place that is causing problems with some inbound email to us from the internet. It is casuing a "sender timeout" message on the Barracuda spam firewall.
I was able to correlate the following messages from the log with the sender timeouts. It appears that the ASA is denying the traffic after the intial connection.
Here are a couple of log messages. It starts out with the ASA tearing down the connection and then denying the next packet in.
1. Teardown TCP connection 67287318 for outside:82.x.y.z/2793 to inside:10.a.b.c/25 duration 0:00:01 bytes 187 TCP FINs
2. Deny TCP (no connection) from 82.x.y.z/2793 to 63.a.b.c/25 flags FIN ACK on interface outside