Recipient address rejected (Full Version)

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Laguna -> Recipient address rejected (24.Jun.2008 2:46:08 PM)

I am having issues with the seemingly famous SMTP 5.5.1 error.  My Exchange server immediately pumps back this NDR:

Your message did not reach some or all of the intended recipients.


Sent: 6/24/2008 11:29 AM

The following recipient(s) could not be reached:

'' on 6/24/2008 11:29 AM

The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address.

< #5.1.1 smtp;550 5.1.1 <>: Recipient address rejected: User unknown in relay recipient table>

The catch is it only happens when we send to two domains (that we know of).  We can send anywhere else on the internet without problems.  The NDR is returned immediately, which makes me think that it is not leaving our Exchange server and getting out to the internet... which means our Exchange server is rejecting this recipient for some reason completely unknown to me.

We use a whitelist but no blacklist.  Relaying is restricted to authenticated users.  Client site has whitelisted our domain.  I've tried several things I've found on the 'net to no avail. 

Please help, the bosses are circling.

uemurad -> RE: Recipient address rejected (24.Jun.2008 2:48:51 PM)

This is caused by a filter on the receiving system.  If the address isn't included in their "allowed recipient" list, this is the sort of message that comes back.

Laguna -> RE: Recipient address rejected (24.Jun.2008 2:52:02 PM)

Thanks Dean.  They have completely whitelisted my domain.  Since the NDRs show up immediately, and since my POP3 connector only checks each mailbox for mail every 3-5 minutes, there's just no way I can see that these NDRs are being returned from the internet; they almost have to be coming from either my Exchange server or are a result of my external mail server (hosted by another company) not accepting the email.  Am I way off track?

hscsadmin -> RE: Recipient address rejected (24.Jun.2008 3:06:17 PM)


my external mail server (hosted by another company)

Sounds like a place where to look for an answer [image][/image].

Laguna -> RE: Recipient address rejected (24.Jun.2008 3:11:23 PM)

That's fine -- I have definitely contacted them and gotten no love -- but I guess my question is this:

Is there ANYTHING on my Exchange 2003 server that I could possibly have misconfigured that would lead to this?

hscsadmin -> RE: Recipient address rejected (24.Jun.2008 3:22:14 PM)

Here is what I could think of:

1. Double-Triple verify that destination server is not blocking. As a reverse test try to send something from outside mailbox (gmail, yahoo) and ask them to temporarily block and then after you receive NDR message whitelist your particular email address that you are going to be using just to test how well their filters respond.

2. Check settings on your relaying it sounds like emails don't even reach the target domain and are being rejected after they are relayed.

Please let us know if you find the cause. I am intrigued now.

uemurad -> RE: Recipient address rejected (24.Jun.2008 3:45:23 PM)

The simplest way to verify what is going on is by performing a telnet test to one of the troublesome domains.  I wrote some instructions you can follow.

What I expect is that you will get a non-OK response to the RCPT TO: command.
This is likely independent of them whitelisting you.  It sounds more like they have neglected to add some of their people to their own approved recipients list (regardless of whether you are on their approved or blocked sender list).

hscsadmin -> RE: Recipient address rejected (24.Jun.2008 4:45:57 PM)

We've have a similar problem some time ago. While we thought we have whitelisted some senders their message were still dropped. They have to add IP address of the mail server you relaying all the email to into their IP trusted list on the server that filters incoming messages. If your domain reputation score is too low even though they whitelist you from their spam filter dictioneries it may still reject eh messaged.

Its arguable though, depends on what kind of filtering system their domain is using. But do that telnet test first. And then verify that recipient server filtering system has whitelisted IP address of the email server, and not your email server but the one you relaying messages to since that server plays a role of a main "sender". Its possible that both yours and relay servers IPs need to be whitelisted. Just a thought.

Laguna -> RE: Recipient address rejected (25.Jun.2008 8:27:05 AM)

I have my answer, and resolution.  What a burden lifted.  Here's the scoop:

Our Exchange 2003 server is internal.  One domain. Forward all non-domain emails to a smart host that our web hosting company provides.  Web hosting company also owns our internet email addresses; we use a POP3 retriever app to go fetch the mail from their server and put it into the right Exchange mailboxes.

Web host USED to also host the company we couldn't send email to.  When that company left for another web host, our web host didn't properly clean up their records (including MX), so when my company would attempt to send email to the other company, our web host's MX records indicated they owned the receiving domain, but since no email accounts were set up any more, we were immediately returned the 550 5.5.1 error: no user exists.

Web host cleaned up their records, and shazam, we can send email to the other company.

I have never seen this as a problem/resolution on the web (and believe me, I've searched), so hopefully this will help someone else with a less-than-ideal web hosting company.

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