Why do I get 550 5.1.1 Usaer unknown message ??

[countrydj]

Hi...
I am using Centos 5 on my linux server.

This is my problem:
Using my own server's SMTP (Relaying is allowed from my ip number),if I send an email, using Eudora or any other mail client, to one of my customers it will not send. It gives a 550 5.1.1 User unknown message.
I can send email to any of my other clients without problem.

Using my ISP smtp server, the same email will send and is received by the client.

There is obviously something missing on my server that is refusing to accept this particular email address.

Can anybody suggest anything that may cause this to happen???

Thanks,

John C

[falko]

Can you post an excerpt of your mail log when this happens?
Which MTA are you using? Postfix or Sendmail?

[countrydj]

Hi Falko...
Many thanks for your replied to this problem.

I have now solved the problem:

hisdomain1.com was listed in local-host-names

The domain is not hosted on the sending server.
It seems that the sending server checked and found hisdomain1.com was listed in local-host-names, but could not find the user on the server, so returned a 550 5.1.1 error.

Since hisdomain1.com was listed in local-host-names
on the server that hosts the domain, there was no problem with any other sender getting mail through.

Hope this makes sense...

Thanks for your help

John C