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Peter_CullFlag for United Kingdom of Great Britain and Northern Ireland

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Exchange 2003 #5.5.0 smtp;550-Verification failed

When one of my users sends email to an external email address they get:
There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
<SERVER.DOMAIN #5.5.0 smtp;550-Verification failed for <>>

This has happened 4 times.  I can send email from the users PC using his email account to my HOTMAIL address and that works OK.  I can also send mail to the same external address from my PC using my email account and it works OK.  But when I send mail using my PC and his email account to the external email address I get the same error.

The error message is coming from my exchange server.  If this were a DNS issue surely I wouln't be able to send mail from my email account.  Hope this makes sense.

Any help would be appreciated.  Thanks.
Avatar of Sembee
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The error message is being generated by your server because the remote server is rejecting the message. The most efficient way of dealing with spam is not to allow the email to be delivered and the sending server to generate the NDR - which is what is happening here.

The remote server is trying to verify the user exists on the server sending the message, which is a suspect method of spam detection as not all messages come from a server that accepts email for that user. A bit of a mystery why it works for one account and not for another.
Anything different about the account in any way?


If your question has been answered, pleased remember to accept the answer and close the question.
Avatar of Peter_Cull


Hi Sembee,

Thanks for the reply, I didn't realise the NDR could come from my own server even though the remote server rejected the message.

I've discovered it's not the user being blocked but their email domain.  Our email server has multiple domains, one per company i.e., etc.  I changed the users primary SMTP address to an address with a different domain and the email got through.  I had the same result changing my own account.

Could this be caused by the recipient email server not recognising my domain due to DNS issues?
Avatar of Sembee
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