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Exchange 2003 5.5.0 smtp;551 User not local. Authentication required for relay

Hi All,

I am getting the following error while trying to send an email to some with an @alonso.tv email address.

5.5.0 smtp;551 User not local.  Authentication required for relay

I am using Exchange 2003 and I have no issues sending to other external accounts.  I also did a mail trace and I get the error exactly when it tries to leave the server.  

 I am not sure what is going on

Thank you for all of your help in advance

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thomasm1948
Asked:
thomasm1948
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2 Solutions
 
slappy901iCommented:
That means that the user does not have an account on their server alonso.tv. Check your recipeints email address and verify with the recipient.

The reason why it is asking for authentication is because the host doesn't recognize the user@domain and wants to relay to another server. :)
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thomasm1948Author Commented:
hmm, we received an email from the the person from @alonso.tv.  If the user did not have an account from @alonso.tv then we should get an NDR indicating that the user does not exist their.

I also did a ping to alonso.tv and it resolves to a public IP
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tigermattCommented:

That isn't a typical Exchange message, so it is being generated by some other MTA along the route.

It would indicate either the MX records for alonso.tv are incorrect (so email is being sent to the wrong server) or the server which is receiving the email isn't configured correctly. "User not local" suggests it doesn't know about the entire email domain, and therefore stops processing the message (if it continued, it would be an open relay... and a spammer's dream).

There is a small possibility your server is configured incorrectly. Check you don't have an SMTP connector configured which has alonso.tv as its address space (in ESM, under your Routing Group > Connectors). It could be such a connector is transmitting email to the wrong server, which would cause this, but unless you have dealt with this domain before, I doubt this is the case.

I suspect the issue lies in the recipient's configuration. It might be temporary (during a server move at their end or something), so if nothing else works, take it up with their postmaster or try again later.

I did try to look up the MX records for alonso.tv, but it doesn't appear to be a valid domain. I presume you changed the actual domain when you posted the question here?

Matt
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slappy901iCommented:
User not local.  Means the server doesn't recognize the user.
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tigermattCommented:

Sorry, comments came in while I was typing mine.

>> If the user did not have an account from @alonso.tv then we should get an NDR indicating that the user does not exist their

Receiving a message purporting to be from a user and sending an email back to that user are two different things.

Anyone can make a message appear to come from an address that doesn't exist. Take Experts Exchange - they send all their emails about comment notifications, new questions etc. from noreply at experts-exchange.com. That is valid for sending, but it doesn't necessarily have to exist as a mailbox to receive emails inbound.

Like I said, it sounds like the server at their end is configured incorrectly. There's a small chance it's your server's send connectors, but given the number of times I've dealt with SMTP mailflow issues like this, I'd say that's unlikely.

Matt
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slappy901iCommented:
I agree with tigermatt. I do not think it is a problem with your mail server.
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thomasm1948Author Commented:
alonso.tv is the correct domain.  I did not use an actual user.  why would it resolve to a public IP if it is not a valid domain
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slappy901iCommented:
Because someone could have setup a bad dns entry. I see it all the time. I am trying to resolve using my DNS, as well as other DNS servers and no luck resolving that domain name. check your c:\windows\system32\drivers\etc\hosts file and make sure you don't have some type of entry pointing to alonso.tv.

Just a thought.
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thomasm1948Author Commented:
Interesting.  I just tried to email the person from my gmail account and I have not received an error yet, but I figure that I will wait and see if I do.

I also checked MXtoolbox.com and some other MX record lookup site that I found on google and it seems that there is no MX records for this domain.

Thank you both for your help and I will keep this you bosted on if I get an error message from google mail
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thomasm1948Author Commented:
OK, I was able to email the user from my gmail account and I did get a reply from the user.  why would it work from gmail and not my Exchange server
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thomasm1948Author Commented:
Also, one thing to note.  We do not have any router connectors configured on our exchange server.  We only have one in the organization.
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IT-Monkey-DaveCommented:
Interesting.  If I send a test email through our system to a known-bad username at a good domain, like somerandomuser5678@comcast.net, I get this NDR, similar to the SMTP codes you are getting.

#5.1.1 smtp;550 5.1.1 Not our Customer
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thomasm1948Author Commented:
Not our customer sounds correct.  I have received emails before that indicate that a user does not exist but not a relay error and it is interesting that I can email the person from gmail.

Another interesting thing is mxtoolbox.com cannot find any MX records assocaited with it; it just keeps on trying to find something
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tigermattCommented:

I still can't get the domain alonso.tv to resolve, either A records or MX records.

I therefore can't explain why Gmail will deliver email for that domain. The only possible solution is the user is registered with Google Apps for their email (so Google knows of their domain, their mailbox and will deliver) but they don't have the correct DNS setup for anyone outside Gmail to deliver email to them.

The errors between an "unknown user" and an "unknown domain" are usually very different. Unknown user suggests you've hit the right mail server for that domain, but it won't deliver because the mailbox doesn't exist. It'll do this as opposed to sender an NDR, because the latter can be exploited to cause backscatter. By contact, an unknown domain error might say just that, or give a message about being unable to relay; if it doesn't know of the WHOLE domain, the server would have to contact another to pass the message on, a job usually reserved for open relays (bad), an ISP's outbound SMTP servers (usually require authentication) or a user on the server sending an email message.

It could be a faulty Exchange configuration as I detailed in an earlier comment. It's possible it's an issue with the receiver's DNS. Perhaps they have moved to a new mail system (such as Google Apps) but not made the required back-end changes.

Matt
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tigermattCommented:

If there's no MX record, the RFCs are such that it should try to find an A record (i.e. the A record for alonso.tv) and attempt delivery there.

I can't find an A record for that domain either, though, and I'd expect MXToolbox to be built with this clause of the RFC in mind.

Matt
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