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

Posted on 2014-10-27
Medium Priority
Last Modified: 2014-11-04
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
Question by:cookd47
  • 3
LVL 45

Expert Comment

ID: 40406705
Looks like DNS issue...anything change recently?
LVL 45

Expert Comment

ID: 40406710

Author Comment

ID: 40414468
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
LVL 45

Accepted Solution

Amit earned 2000 total points
ID: 40415051
Error also says connection issue, if no issue currently then u can consider it as resolved

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