smtp;450 error

[chris4ops]

Hi all,

A client keeps getting this message from their SMTP:

########################################################

Reporting-MTA: dns;XXX.XXX.XXXX.XXX
Received-From-MTA: dns;KTES2292EVSS525.XXX.XX.XXXX.XXX
Arrival-Date: Thu, 7 Aug 2008 20:06:45 +0200

Final-Recipient: rfc822;xxxxx@yyyyyyyyy.com
Action: delayed
Status: 4.0.0
Diagnostic-Code: smtp;450 <xxx.xxxxx@xxx.xxxx.xxx>: Sender address rejected: Domain not found
Will-Retry-Until: Sat, 9 Aug 2008 20:06:45 +0200

###########################################################

Nobody from their domain can send it to anyone on our domain. Their thought is the problem is with our "digital signature" which i'm not sure how to change/modify. We use SunOS 5.8 mailx pop3. And i'm pretty sure they are using sendmail. I tryed adding their domains to our spam filter white list, but that did not solve the problem, i'm pretty new with linux servers so i'm not sure where to go from here. I'm also not sure if theres a problem with their sendmail or our pop3.

Any help would be greatly appreciated.
Thanks

 

[elgrandeperro]

Forget pop3, that is the "getting" of mail.

Is the report-MTA yours?

After the 450, after the @ sign, is that a valid domain or subdomain or host, and does it have MX records? Is you MTA accepting mail for that exact host/subdomain?

 

[chris4ops]

No, this is a report the customer received from their SMTP. I originally thought it was on their end, but my boss kept pestering me that he "NEEDS" to get those e-mails from them, so I was looking for any possible wrong-doing on our end.

Yes it is a valid domain after the @ sign, spelling is correct. We used to be able to receive from them, but the past month we have not been able too. And they are able to receive e-mail fine from us.

I'm not really sure how to check MX records, i'm a complete newbie with smtp, and especially linux servers. The previous guy never showed me around them.

Thank you for your input, it gives me some things I can research to look for.