The error message "Remote Server returned '554 4.4.2 < #4.4.2 X-Postfix; conversation with {cisco spam gateway} timed out while receiving the initial server greeting>" indicates that the remote server (in this case, the Cisco Spam Gateway) did not respond within a reasonable time during the email conversation.
In this scenario, it's indeed possible that a network issue, or perhaps an issue with the Cisco Spam Gateway, caused the timeout.
Look for entries related to the error code 554 4.4.2. on mail_logs
Packet capturing can be very useful in troubleshooting network-related issues, including email delivery problems like the one you're experiencing.
