Ok, so we are using Barrcuda email security to route incoming mail to our 2013 Exchange server.
All of a sudden yesterday we started to see Deferred (451 No response to HELO/EHLO) in Barrcuda, so I opened a support call and was told
"That means that the recipient mail server is rejecting the email for that reason. We just relay back the answer to the sender mail server. The delivery status is always what we get back. The action is allowed, which means the Barracuda would have allowed that message. "
So I've run the Exchange Connectivity Test for a could of email address and I get the following error...
Attempting to send a test email message to firstname.lastname@example.org using MX d51832a.ess.barracudanetworks.com.
Delivery of the test email message failed.
The server returned status code 451 - Error in processing. The server response was: No response to HELO/EHLO Exception details: Message: Error in processing. The server response was: No response to HELO/EHLO Type: System.Net.Mail.SmtpException Stack trace: at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.RecipientCommand.Send(SmtpConnection conn, String to, String& response) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at Microsoft.Exchange.Tools.ExRca.Tests.SmtpMessageTest.PerformTestReally()
Elapsed Time: 534 ms.
Nothing changed on the exchange server apart from last week I upped the message limit from 10MB to 30MB, but that was last week.
I am stuck now what exactly does 451 No response to HELO/EHLO on incoming email mean and where would one start to trouble shoot such a problem
I can TELNET onto the exchange server from within side the LAN