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

It does send but it bounces. The 550 comes from the receiving end (as far as I know). Contact the administrator of the receiving end.

Just to clarify....

It doesn't send from my mail client when using my own SMTP server

When I use my ISP SMTP server the mail is sent OK and is received by the recipient.

I am the administrator of my own SMTP server.

This is why I am puzzled by the error.

hth

John C

I don't run my own mail server and I don't have much knowledge about them so maybe the previous post should not have been so 'absolute'. This is my story:

I once got 550 messages back (not 5.1.1, I think it was a 5.7.6) when I was sending emails to certain email addresses using my ISPs smtp server. I was however able to send to those email addresses using another way (same as you). Some research revealed that my ISP's smtp server was blacklisted.

So that makes me think that the 550 does not (necessarily) come from your mail server but from the receiving mail server. And therefore it can not harm to contact them.

Before I posted my previous reply, I tried to do some research on the internet for your error message, and everything I read did point to a reply from the receiving mail server (mailserver.otherdomain) and not of your mail server (smtp.yourdomain).

Hi Wim...
Thanks for taking the time to reply.
I'm sure that you are right that 550 comes from the receiving server.
However, in this case I believe that it is MY server that is the receiving server.
i.e. the mail does not get any further than my server.
I believe that the mail must be looking for the recipient on my server and not finding it so therefore bouncing the mail.

My reasoning is this:
I can send an email to customer1@hisdomain and it goes through.
I can send an email to customer2@hisdomain and it DOES NOT go through.

Both these are my customers, and I host their web sites and mail boxes.
Therefore there must be something on my server that is preventing this from happening.

Do you follow my reasoning ???

John C

Why don't you check the log files? /var/log/maillog on Redhat flavors. Or try doing this from console (commands are written in bold).

You will probably find the issue while doing the above exercise.

Thanks
Salih

OK, I did not realize that the receiving email address was on your server.

Sorry if I put you on the wrong track.

Hi Salih..

Thanks for taking the time to read and respond to my post.

I went through the instructions that you suggested.
It all went well.
I got to the end and placed a "." on a new line and got the following response:
250 2.0.0 n579nBC2013598 Message accepted for delivery

It just sat there until I typed quit.

I checked the maillog on both sending and receiving servers and nothing showed.

Any thoughts on this ???

John C

Many thanks to the people who replied to this problem.

I have now solved the problem:

hisdomain1.com was listed in local-host-names

hisdomain2.com was NOT listed in local-host-names

Neither domains are 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