Some inbound emails are being blocked by spam service in the SMTP session. 

The recipient can see error "qq write error or disk full (#4.3.0)" within the log of Track and Trace.

qq write error or disk full (#4.3.0)

Disk error occurs in the remote Symantec server and the issue is under investigation.

The recipient can check this error in the row “Service Reason” of Track and Track log.
Meanwhile, 451 error returns to the sending server and the sending server will resend the mail according to their retry schedule.

Sorry for the inconvenience that may have caused to you. Symantec is aware of this issue and will update this document when a solution becomes available.
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