#5.7.1 smtp;550 5.7.1 Unable to relay

[WinNT511]

We have serveral regional mailboxes on our exchange server and one domain is having problems sending email to a particular mailbox (Region5@domain.com). this mailbox can receive all other email from different domains with no problem.

The sender receives the following error message:

The following recipient(s) could not be reached:

(external for mydomain.com) on 9/26/2007 12:08 PM
You do not have permission to send to this recipient. For assistance, contact your system administrator.
<senderdomain.com #5.7.1 smtp;550 5.7.1 Unable to relay for Region5@mydomain.com>

The Exchange Server is completely up to date with patches and updates. I have checked both DNS Servers and records with no problems indicated. I have sent test message to the mailbox with no problems indicated. I believe the problem is on the sending domain but there tech insists it is on my end?

Can someone please help?

WINNT511

 

[WinNT511]

Should the relay box be checked or unchecked under the SMTP Virtual Server? and if it is checked would it cause the error message the sender gets when sending mail to Region5?

This setting is checked by default.

Launch Exchange System Manager (ESM) and navigate to the SMTP virtual server you are using to send messages to the Internet. View Properties -> Access -> Relay and ensure that the "Allow computers which successfully authenticate to relay" checkbox is not checked. - I read this and it says it should be unchecked?

Please advise,

WINNT511