Exchange 2013 - Help with 451 No response to HELO/EHLO on incoming email

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 using MX
Delivery of the test email message failed.
Additional Details
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



Ian PriceIT ManagerAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Can you telnet from your exchange server to you barracuda device over port 25? If so, can you issue helo and get good response? Also, can you somehow test port 25 to your mail server from your barracuda device somehow?
Zacharia KurianAdministrator- Data Center & NetworkCommented:
A couple of tests/matters to follow;

1. Test if you could telnet to your exchange from outside your LAN.
2. See if your MX records are not black listed.
3. See if your MX holds proper PTR records.
4. If you have a SSL cert for your exchange, make sure it is not expired.

Had a similar post but with exchange 2010. Might help you out.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Ian PriceIT ManagerAuthor Commented:
How do I

See if your MX records are not black listed.
See if your MX holds proper PTR records.


It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.