I think my server is under such attack mentioned below :

there are about 400,000 mails in queue and mail server can not handle such huge mails and it is so slow and even local mails don't work.

How can I ban domains like msa.hinet.net , yahoo.com.tw , etc?

I entered zimbra administration website on port 7071, and go to the mail queue page, but I can not delete that huge mail with web interface and it says me :

Server error encountered Message: system failure: exception occurred performing queue action Error code: service.FAILURE Method: MailQueueActionRequest Details:soap:Receiver

please help me, I don't know how I can back to the normal state.