You want to Wireshark to capture infromation about your traffic through the Email Security.cloud service.
To run Wireshark
If any packets miss or information is garbled, it is clear that something was lost in transit. Packets that are displayed in red text on a black background usually indicate a problem.
"TCP RETRANSMISSION" error means that a packet was lost in transit, and TCP had to recover by resending the packet. Too many retransmission may indicate a larger problem such as poor link quality or latency.
"DUPLICATE ACK" indicates a more serious problem as it means that the ‘ACK’ (acknowledgment) packet took so long to travel that another one was sent. Now the receiver sees the packet again.