Mail Failure Notice due to unknown email address on list

[cbminstrel80]

Hi there,

I set up a mailing list of sorts on my site. It wouldn't work using 'sendmail' so I had to set it up as a stmp.

It's been working fine until yesterday one of my site users got this email when they sent a post to the list:

---------- Forwarded message ----------
From: <MAILER-DAEMON@outgoing.x10hosting.com>
Date: Wed, Jun 22, 2011 at 1:41 PM
Subject: failure notice
To: xxx


Hi. This is the qmail-send program at outgoing.x10hosting.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<datingdoor@datedirect.com>:
Sorry, I wasn't able to establish an SMTP connection. (#4.4.1)
I'm not going to try again; this message has been in the queue too long.

<datingdoor@datedirect.com>:
Sorry, I wasn't able to establish an SMTP connection. (#4.4.1)
I'm not going to try again; this message has been in the queue too long.

--- Below this line is a copy of the message.

Now, I've checked....this email address isn't on my users lists so wasn't added via the website. The address also isn't even in the list of email addresses listed at the top of the message 'shown below the line' for the message to be posted to. So how/why is my mail trying to post with it?

The stmp is set up through my email account I set up on my webhosting account, however it's completely empty, no addresses, no forwarders as I purely use it to run the mailing list through.

Any thoughts?

[vv.bbcc19]

I am not sure of the problem but when such problems happen, it is easy to rebuild than debug as some small mistake could create all the trouble.
This a basic tutorial from cpanel software makers.This is all on mailing list - how to etc.
Hope this helps.