Icewarp mail server error during SMTP protocol

Hi,

Our server some time gets trouble in receiving email from remote SMTP server.

Capturing the packets to investigate, I found: sometimes my server takes about 1 minute to send a response packet after receiving data from a remote SMTP server. It causes the remote SMTP server to time out and then it actively disconnects so that the message cannot be forwarded successfully.
Meanwhile, the remote SMTP server sent several messages, all with the same error.
This error is only fixed by restarting the SMTP service on my server or on the remote server.
Please asist me handling this issue
I enclose the image for your evaluation.

Thanks

Phạm Minh Toàn