An email sent outbound by one of your users is bounced back by Symantec.Cloud advising that the message could not be delivered.

This is the mail delivery agent at messagelabs.com.

I was unable to deliver your message to the following addresses:

This bounceback indicates that we accepted the message but we could not deliver it to the intended recipient server. We will include the refusal message that the recipient server provided which is the best source of information regarding the cause of the rejection.  Some examples of issues and corresponding error messages:

• The email was larger than the recipient server will accept:
  • 552 5.3.4 Message size exceeds fixed maximum message size
  • 552 Message size exceeds fixed limit​

• The recipient's mailbox is full:
  • 552 Mailbox is full
  • 552 Requested mail action aborted: exceeded storage allocation​ 

• The recipient address isn't one registered on the recipient server:
  • 550 User unknown 
  • 554 5.7.1 Recipient address rejected: No such user​

• The recipient server is not configured to accept mail for the recipient domain:
  • 550 5.7.1 Unable to Relay 
  • 554 5.7.1 Relay access denied

• The recipient server finds something suspicious in the message content:
  • 550 5.7.1 Message rejected as spam by Content Filtering. 
  • 554 Denied (Mode: normal) 
  • 550 Denied by policy
  • 552 MS-Office file containing VBA macros found inside of the email 
  • 550 5.7.1 Message rejected due to content restrictions

• The recipient server has an issue with the sending email address:
  • 554 5.1.0 Sender denied 
  • 553 Envelope sender rejected 

• The sending server cannot be seen as authorized for the sending domain:
  • 550 SPF check failed. Sender not authorized 
  • 550 Sender verify failed 
  • 550 5.7.1 SPF unauthorized mail is prohibited. 

• There was a temporary issue on the recipient server that was not resolved before the message retry time expired:
  • 554 5.4.7 [internal] exceeded max time without delivery 

Please note that this list is not exhaustive and the error messages from a server may not match exactly to the above, though they are often very similar.

The majority of these issues must be resolved on the recipient system as it is that system that is refusing the messages.  It is also possible in some cases that you might need to confirm the recipient's email address or adjust the message content to prevent it from being blocked by the recipient server.

If you are unsure if the bounce is due to Symantec Email Security.Cloud blocking the mail, you can use Track and Trace to search for the particular email and review scanning service and delivery information to confirm this information.

In the case of SPF/Sender verification issues, you might need to implement or adjust your SPF Record.  Please see: https://support.symantec.com/en_US/article.TECH226211.html

If you are unable to identify the cause for the message failure, please open a case with Symantec Technical Support and we can assist in understanding the issue with troubleshooting and message logs and advise what might be needed to resolve the issue.