One more suggestion. I see that the IP address 222.67.186.87 is black listed on SpamHaus XBL. You could add an XBL filter in Xeams using the following configuration:

VERY IMPORTANT: Under normal circumstances we do NOT recommend checking the "Check only first IP in the header" box. That can result in many false positives. However, since you're under attack, do this temporarily and remove it once done.

You could also enable RBLServer.log in Xeams. Check https://xeams.com/xeams-log-files.htm , select the tab for Additional Logging and see RBL Servers.