550 Your host is not allowed to connect to this server.

This is for a shared server for which I am the admin. It's semi-managed elsewhere for hardware, but software issues usually fall on me.

As of yesterday, two clients have reported the same problem. Several of their customers from overseas have tried emailing them, but get the following error:

Code:

550 Your host is not allowed to connect to this server.

Connection to host lost.

This has been reported from one email sender from Brazil, another from Hong Kong, and another from Malaysia. Remember, these are external people getting an error when emailing my client, but the client has no error when emailing back. Running a trace through WHM returns with no errors.

I don't see any of the IPs listed in cpHulk or CSF. As a test, I completely disabled CSF for this server and asked the one from Malaysia to try again, but he's still getting the same error.

Presumably, this problem didn't exist until yesterday.

Any suggestions on what the problem might be, if it's not CSF or cpHulk?

 

To my knowledge, the only place that checks RBLs is the CSF firewall (which is now disabled). Unless SpamAssassin does it? I have no idea how to check or change that.

I had compared the ones reported to MXToolbox before. One of them was listed in a blacklist for which I am unfamiliar, but their Senderbase.org reputation was "Good" so I don't know if that's relevant. All of the others that I checked came back with a clean record.

 

The problem continues! Today, I tried sending an email through Quickbooks to a customer, which uses a separate server than the one in the OP. This one bounced with the following (where example.com = me, example2.com = recipient, and 1.2.3.4 = my IP):

Code:

From: Mail Delivery System [mailto:Mailer-Daemon@example.com] 
Sent: Thursday, February 02, 2012 10:29 PM
To: me@example.com
Subject: Mail delivery failed: returning message to sender

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:

  recipient@example2.com
    SMTP error from remote mail server after RCPT
TO:<recipient@example2.com>:
    host extrpfx3.extrasecurity.com [67.29.153.36]:
    521 5.7.1 <example.com[1.2.3.4]>:
    Client host rejected: server ip location rejected, only accepts usa

My server is with Softlayer, and is definitely located in the US.

Does it look like it was rejected by MY server, or the recipients? If it was rejected by my server, presumably because it went through Quickbooks, then how do I whitelist it so that it's no longer rejected? Obviously, being able to send emails through Quickbooks is quite important!