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

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

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

User not local.  Means the server doesn't recognize the user.

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

I agree with tigermatt. I do not think it is a problem with your mail server.

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

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.

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

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

Also, one thing to note.  We do not have any router connectors configured on our exchange server.  We only have one in the organization.

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

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

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