503 5.5.2 Send hello first

We have just inherited a customer who have a Front-End and Back-End exchange configuration. Intermittently senders receive a bounce back from the Front-End server with the error 503 5.5.2 Send hello first.
Mail delivered to this customer goes through a 3rd party who run a smarthost service  in a ‘filter and forward’ setup.
As this is an intermittent problem we are not sure where to start looking.

Any help would be much appreciated.
omnisysAsked:
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MegaNuk3Commented:
It's probably not the front-end server doing that. It s most likely the 3rd party smarthost service. Some anti-spam engines prefer HELO to EHLO.
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omnisysAuthor Commented:
Thanks for that. This is something we suspected but the 3rd party are adamant that this is a local server problem. Is there anyway we can prove this?
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MegaNuk3Commented:
telnet into it on port 25 and see what the banner says.

then do EHLO yourdomain.com and see what it says
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MegaNuk3Commented:
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omnisysAuthor Commented:
Thanks again for your prompt response!

We are unable to send any commands. As soon as we type the 'e' of ehlo we loose the connection. See below. Is this significant?

220 mail.domain.co.uk Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959
ready at  Mon, 12 Apr 2010 13:53:22 +0100
e

Connection to host lost.

Press any key to continue...
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MegaNuk3Commented:
what happens if you start typing HELO?
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MegaNuk3Commented:
where are you telnetting to? the external IP address of your MX record? i.e. the Smarthost or the front-end server?

The FE is probably setup to only accept connections from the smarthost and the BE servers.
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omnisysAuthor Commented:
When you type anything it drops the connection.

The MX record points to the 3rd party. We are telneting onto the FE's IP. You are probably right that it only accepts connections from the 3rd party.

For the purpose of troubleshooting would we change the setting in System Manager on the FE?
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MegaNuk3Commented:
you should be able to telnet from the BE to the FE to prove it isn't the FE
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MegaNuk3Commented:
you can also test telnetting to the 3rd party smart host and see if it accepts EHLO or not.
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MegaNuk3Commented:
To telnet to the SmartHost though, you are probably going to need to do it from the FE if the smarthost has IP address restrictions in place.
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omnisysAuthor Commented:
Below is BE telnetting onto FE:

220 mail.domain.co.uk Microsoft ESMTP MAIL Service, Version: 6.0.37
ready at  Mon, 12 Apr 2010 14:53:34 +0100
EHLO exchange.domain.local
250-mail.domain.co.uk Hello [10.0.0.41]
250-TURN
250-SIZE
250-ETRN
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-8bitmime
250-BINARYMIME
250-CHUNKING
250-VRFY
250-X-EXPS GSSAPI NTLM LOGIN
250-X-EXPS=LOGIN
250-AUTH GSSAPI NTLM LOGIN
250-AUTH=LOGIN
250-X-LINK2STATE
250-XEXCH50
250 OK
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omnisysAuthor Commented:
We can't send any telnet commands to the 3 servers that the MX record points to at the 3rd party. The connection just drops.
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MegaNuk3Commented:
Have you tried from the FE telnetting into the IP address listed as the smarthost on the SMTP connector?
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MegaNuk3Commented:
but effectively by telnetting into the FE from the BE you have proved your FE accepts EHLO, so that should be enough proof for the 3rd party.
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omnisysAuthor Commented:
This exposes our lack of understanding as we assumed the smart host in the smtp connector was for outgoing mail only. For what it's worth the smart host drops the telnet session when any command is typed too.
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MegaNuk3Commented:
where do the MX records for the e-mail domain hosted by the BE/FE point to? Is that IP address this 3rd party spam solution? If so then that 3rd party is for incoming mail too.

did you telnet the smart host from the front-end server?
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omnisysAuthor Commented:
The MX record points to 3 servers at the 3rd party spam solution.

Yes we did telnet from the FE to the smarthost.
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MegaNuk3Commented:
maybe one of the 3 is giving the "send HELO first" error and that is why you are getting it periodically...

It's definitely not Exchange as all MS Exchange/SMTP servers accept EHLO:
"You can use the HELO command, but EHLO is a verb that exists in the Extended SMTP verb set that is supported in all current Microsoft implementations of SMTP." from http://support.microsoft.com/kb/153119/en-us
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MegaNuk3Commented:
Thanks for the points. Was it the 3rd part servers in the end?
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