The vpxd.log file contains entry similar to:
<YYY-MM-DD>T<time> [05596 error 'win32vpxdMail_win32' opID=task-internal-17210-c6506a65] [VpxdMail] Failed to send the mail to SMTP server 10.10.10.10 at port 25. Error=The transport failed to connect to the server.-->
</time>