inbound messages returned with error: 451 Cannot establish backend connection (2)

We are running Exchange 2010 and have a SonicWall  TZ210
Some senders to our organization are getting messages returned with the following error
A temporary error occurred while delivering to the following address(es):

  <user1@domain.com>: 451 Cannot establish backend connection (2)
  <user2@domain.com>: 451 Cannot establish backend connection (2)

I will continue trying to send the message until it is delivered or expires.

Not sure how many were returned
cookd47Asked:
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AmitIT ArchitectCommented:
Looks like DNS issue...anything change recently?
0
cookd47Author Commented:
The problem seemed to be the result of a connectivity issue last Friday, no issue at this time
These were not distribution groups, but email sent to multiple recipients (CC); Reports showed 130 emails wee returned, I suspect that most eventually were resent by Exchange or Message service and delivered; the connectivity problem only lasted a few hours
0
AmitIT ArchitectCommented:
Error also says connection issue, if no issue currently then u can consider it as resolved
0

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