Mailbox Unable to receive EMail

I am using a xMatters interface to connect with my internal employees.  Over the past few weeks we have started to received thousands upon thousands of bounce messages from with the Subject line "Mailbox Unable To Receive EMail".  (Over 21,000 messages in the last 12 hours)

As a good corporate citizen, I want to ensure that my system is not sending messages to the wrong address so I go to investigate.  Looking at the message below, I am not sure what I can do.   Anyone here have an idea of what to do?

Error: Invalid user address

Error message below:

550 - Requested action not taken: no such user here

Message details:

  Subject: Mailbox Unable To Receive EMail Messages

  Sent date: Fri Mar 22 00:34:46 GMT 2013



  From: "" <>

  To: "" <>

  Size (in bytes): 3030

  Number of lines: 94

Labels (1)
Re: Mailbox Unable to receive EMail
Not applicable

When you view a full header of an email that was returned the receiving mail domain checks for a valid address. If this address is not one of their users a bounce message is returned to the sending domain.

The full header gives the reason for the return, this could be for one user or 100,000 users.

In certain situations the senders mail could be rejected due to spamming or the dns of the mailer could be on a block list in which case you need to speak with the NOC at verizon to see what the situation is.

The little bit of information above tells me two things.

1- This was not email but a text or mms send.

2- The persons is not correct you are sending to.

Your admin at your work could call and check with verizon. It may be something as simple as a wrong name or even a wrong syntax to send mail.

Re: Mailbox Unable to receive EMail

Thanks for the response, but there is no information about the phone/text/mms that is failing within the header.  All 30 of the messages that I checked had essentially the same header information. 

Received: from ([]) 

Received: from unknown (HELO VZW) ([])  by

with ESMTP; 22 Mar 2013 10:15:42 +0000

I am sure that my xMatters system has a bad registered phone number.  If this bounce message would tell me which account is failing, then I could do something about it.   All I have is a 350Mb of these messages blocking of my mailbox.