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SMTP Error 550 Unknown user

Posted on 2003-11-27
Medium Priority
Last Modified: 2008-02-01
We have SBS 2000 using Exchanger Server.  It has been working fine for about 7 months.  2 days ago without any notice in event logs, etc. we stopped getting in external email.  There have been no changes to the server or our ISP service, etc.  I've looked at all the settings, etc  and all seems well.  Any ideas?
Question by:kevincavanagh
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LVL 24

Expert Comment

ID: 9832843
could u give more error message.
LVL 24

Expert Comment

ID: 9832864
this kind of error may come for many reason.
relay reason. may be for stopping spam.
please post more error messages from your server logs.
LVL 49

Expert Comment

ID: 9832866

Error message is in the subject

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LVL 24

Expert Comment

ID: 9832891
sunray, thats why i asked "MORE". this is very generic error message and lead to many  possibilities.

Author Comment

ID: 9832999

This is the complete error message I get back when I try to send a message using Hotmail.  You can try from your own email client to see what response you get.  I do not see any errors on the server (I am only looking in the event viewer).  Please let me know what you think...

This is an automatically generated Delivery Status Notification.

Delivery to the following recipients failed.

Reporting-MTA: dns;
Received-From-MTA: dns;
Arrival-Date: Thu, 27 Nov 2003 08:41:47 -0800

Final-Recipient: rfc822;
Action: failed
Status: 5.0.0
Diagnostic-Code: smtp;550 unknown user <>

LVL 31

Expert Comment

ID: 9833013
Doesn't the mail server itself create proper logs? Event viewer may not be enough. Rejection due to unknown user should be in the server log.

Author Comment

ID: 9833031
Where would I look for this log?
LVL 24

Expert Comment

ID: 9833134
could u see some logs from exchange manager.
START  >  PROGRAMS  >   EXCHANGE  >  then then manager program

also could u printout the full header.
this must be in returned mail when u open a mail. there must be option in view -> option
and there must be internet header, post that header.

Expert Comment

ID: 9839003
Do you have a reverse DNS entry for your mail server?  Some sites are using that to determine who is sending spam and then 550's them if they don't have an entry.

Expert Comment

ID: 9879288
maybe its your own computer administrator that prohibited external e-mails. most companies do this to prevent mail saturation.

Accepted Solution

peter_fleur earned 2000 total points
ID: 9923225
If i test it with a telnet to port 25 everything seems to work. It accepted your name. Maybe its a problem at you isp? Did you receive my mail?


Author Comment

ID: 9925318
Hi all,

the problem with this issue turned out to be with one of the ISP's we use who forwards the email to another ISP we use.  They changed the email mx record somewhere along the line and did not realize it.  This is the first time I am using this website for tech answers and you all have been great.  I am not sure what is referred to as "points".  Do I have to decide how to distribute them?  Please advise...thanks again.
LVL 24

Expert Comment

ID: 9925393
Glad u got it resolved.
yes u have to decide how to distribute points or not distribute and give it the one/two...
close the question by following this guidelines:


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