email blocked from sending

[Nexxterra.com]

I have 3 email accounts on 2 different domains that get the error "Recipient error [550 "Unknown User"]" when I attempt to send to only 1 domain.
--If I send to any other domain, it sends fine
--If I create a new email address in either of the 2 domains, the new email sends fine
--This started happening only after the receiving server/domain was down for a few days. (during which emails came back as invalid address)
--The SMTP to this domain is blocked on the originating server, NOT from the receiving server
I believe there is some spam folder or other such type of repository that these addresses have been entered into and I need to clear it manually???

Again, this is 3 email addresses that will not send to any addresses on 1 domain, all other email functions fine outside this issue.
Using a fairly standard DA email install on a centos box.
Any ideas?

 

[nobaloney]

I'm a bit confused.

From your machine to a recipient on a foreign machine?

The foreign machine is replying Unknown User

Or have I missed something?

I'm not sure what Unknown User means in this case. If you can't send email to a particular address on a foreign server from an account on your server, but for example, can from a Gmail email address, then I'd guess that the problem is the recipient box is trying to verify your user exists but for some reason can't.

More info, please.

Jeff

 

[Nexxterra.com]

from my machine to only 1 domain on the other machine.
the message does NOT appear to even be leaving my machine, the returned message appears as I am releasing the mouse button when sending email to the effected address.
It seems like these few emails, while trying to send when the other server had issues, were placed on some kind of list and now will not send to this domain on the other server.
As stated, any new email addresses on the same account will send fine...

------------------------------------------------------------------------------------------------------------------------------------------------
Tried in roundcube and got this, also in an instant... there also does not seem to be mention of the other machine.


Return-path: <>
Envelope-to: [email protected]
Delivery-date: Fri, 30 Aug 2013 12:14:44 -0400
Received: from mail by server.nexxterra.com with local (Exim 4.80.1)
id 1VFRLP-0004bM-U9
for [email protected]; Fri, 30 Aug 2013 12:14:43 -0400
X-Failed-Recipients: [email protected]
Auto-Submitted: auto-replied
From: Mail Delivery System <[email protected]>
To: [email protected]
Subject: Mail delivery failed: returning message to sender
Message-Id: <[email protected]>
Date: Fri, 30 Aug 2013 12:14:43 -0400

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

[email protected]


------ This is a copy of the message, including all the headers. ------

Return-path: <[email protected]>
Received: from localhost ([127.0.0.1] helo=nexxterra.com)
by server.nexxterra.com with esmtpa (Exim 4.80.1)
(envelope-from <[email protected]>)
id 1VFRLP-0004bG-Qd
for [email protected]; Fri, 30 Aug 2013 12:14:43 -0400
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
format=flowed
Content-Transfer-Encoding: 7bit
Date: Fri, 30 Aug 2013 12:14:43 -0400
From: [email protected]
To: [email protected]
Subject: an email test
Message-ID: <[email protected]>
X-Sender: [email protected]
User-Agent: Roundcube Webmail/0.9.1