SMTP Protocol Returned a Permanent Error 503 - Duplicate HELO

Hi,

An external sender received the following error when trying to email a legitimate recipient in my domain:  "Error transferring to MAILSERVER.DOMAIN.COM; SMTP Protocol Returned a Permanent Error 503 mailserver.domain.com Duplicate HELO".

Could this be somehow caused by having multiple Exchange servers in the same Exchange org, with MailMarshal as the relay server to the Internet?
ShepsysAsked:
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.

MaharajkpCommented:
I guess MX is pointing to "MailMarshal" ... and is receiving and forwards emails to Exchange ...
If that's the case and NDR is generated by Exchange ... make sure of Communication between MailMarshal & Exchange

From MailMarshal ... do SMTP Communication Test
Telnet to Port 25 to Test SMTP Communication
http://support.microsoft.com/kb/153119

and try to submit the message
0
ShepsysAuthor Commented:
Correct.  The MX record is pointing to MailMarshal and is forwarding mail to/receiving mail from the Exchange servers.

Telnet tests work fine. This is the only error I have seen like this.  All other email traffic seems to be routing fine.  Just this one particular sender is having a problem.
0
MaharajkpCommented:
If that's the problem then I hope you have tried that telnet test ... with his Email Address on "mail from: ..." ... and if that has worked then you can wash your hands ... its not your exchange problem.

you can carry out that same test from your home machine on your MX record ... and see if that "MailMarshal" is rejecting that message or what

0

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
ShepsysAuthor Commented:
I have verified that telnetting with the sender's info works fine from outside the domain so, as you suggested, it must not be my exchange problem.

Thank you very much for your input.  Will close with an A.
0
ksteirerCommented:
We had a similar problem while using MS SMTP to send 3-4 email into one of our own email servers from a remote location and got around this by putting a 1 second pause between emails. Apparently the spam filter server we use (external provider) mistakenly saw the multiple email connections as a single connection with multiple HELO attempts.

Since this only began occuring at the precise moment the spam filter was enabled (and is corrected by disabled the spam filter) I look at it as a server problem - the spam filter server. It looks like the mail server software is poorly written or set too sensitively (or could have even been designed that way). After all, who wants multiple connects/disconnects to your server every 1/4 second? - this would be similar to a ping attack. Regardless, the only control the user would have, that I see, would be to put pauses between the emails - if they were using a script.

Would anyone have a better insight on this?
0
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
Exchange

From novice to tech pro — start learning today.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.