Recently a client approached us with Mail flow issue with Exchange 2010 SP2 environment, they were unable to receive any emails from Outside (internet) with the following error.
#5.0.0 smtp; 5.3.0 – Other mail system problem 550-‘5.7.1 Anonymous client does not have permissions to send as this sender’ (delivery attempts: 0)> #SMTP#
NDR Received by External users
Delivery has failed to these recipients or groups:
A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.
The following organization rejected your message: [22.214.171.124].
Diagnostic information for administrators:
Generating server: mail.Contoso.com
[126.96.36.199] #<[188.8.131.52] #5.0.0 smtp; 5.3.0 – Other mail system problem 550-‘5.7.1 Anonymous client does not have permissions to send as this sender’ (delivery attempts: 0)> #SMTP#
We found that customer has a sonicwall facing the public IP and it forwards the Port 25 to the HubTransport server. There is more than one transport server in the environment and one of them Failed last night (which used to receive all communication on port 25 TCP from Sonic wall).They have now switched over the port 25 forwarding to the other Hub transport server
We went ahead and validated the receive connectors on the new Hub Transport Server and found that it only has the default recieve connector which doesnt have the Anonymous authentication enabled on it. We enabled the authentication and that resolved the issue.
Please refer to following screenshots for required settings on the Default Receive connector.
Hope this article helps you to fix the critical email down situation you must be facing now. If now, feel free to reach out to us for support here
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