We have an important business contact in China whom we have communicated with by email for years. As of the past few weeks, we cannot send an email to this business successfully. We get the message delayed and then subsequent failed to deliver 4.4.7 message. We are running exchange 2003, and can email anyone else without issue, including other contacts in foreign countries. Also, we can email the important Chinese contact with a gmail account, just not through our corporate exchange.

My conclusion is that "we can email everyone else with no problem from Exchange" and "gmail gets through" = we are being blocked by a spam filter.

Is this a fair conclusion or is there somethign else I can try? Various members of our company have tried emailing the China contact and its all the same NDR. Because of the time difference, we only communicate by email; however in a gmail message we asked them to check their spam filter and they claim they did and its all set.

I think you might have ended up on a email blacklist. Trying to locate which black list you are now on can be difficult. It will effect everyone using the same domain part of the email address (everything after the @) so other people in the company will have the same problem.
You can either find the blacklist and try to get taken off it (there are online tools for that) or wait for the trust level of email address to rise again. That may take some time.
Has your company engaged in any email campaigns later (even legit ones)? Thats how I got pegged a couple of months back.

As for campaigns, we send out of monthly e-newsletter which goes to quite a few recipients. Nothing done commercially, though. I'll try to check out blacklists.


Hericles is probably correct but if your mail is getting through to everyone else you send to, then it could be that they tightened their email servers security, or your mail server does not have a good route to theirs. He is also right that you should verify that there is nothing blocking your server like blacklists or email relay. I would do two things. First go a site like MXtoolbox:


and enter your domain to see if there are any issues with your server. It will check all blacklists and run some tests against your mail server then give you a report and make suggestions on how to correct issues it finds.

It may be that your email server can't get tohas them blocked or is unreachable for some reason. Run these commands from your exchange server as an administrator.

Find out what their MX (mail Exchange) records are set to:

dig -t MX <their domain name>

Like mine comes back with the following:

[root@lptp2 ~]# dig -t MX txlinux.com

; <<>> DiG 9.9.4-P2-RedHat-9.9.4-12.P2.fc20 <<>> -t MX txlinux.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34892
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;txlinux.com.                   IN    MX
ANSWER SECTION:                                                                                                              
txlinux.com.     3600    IN      MX    20    txlinux.com.

txlinux.com.     3600    IN      MX    10    txlinux.com.

Which says my mail server is txlinux.com.

next find out what the domain name resolves for you exchange server using nslookup:

nslookup <domainname>

Finally see if you can get to it either by name or IP address using ping and trace route (or even better WINMTR). WinMTR will show you the riute to their server and any laency or packet loss between the servers.

Hope this helps.

Thanks rch - I'll try this in the morning tomorrow. It is strictly sending emails to this one customer; they can still send emails to us when they initiate the message.