I have an external user (not logged into the domain or LAN) that sends email through my Exchange 2003 mail server. He has a AD user & Exchange account and also a compuserve e-mail account.
When he tries to reply to an email sent to his compuserve account by a customer he gets this NDR:
Arrival-Date: Tue, 27 Nov 2007 16:01:27 +0000
Diagnostic-Code: smtp;550-Callback setup failed while verifying <email@example.com>
550-(result of an earlier callout reused).
550-The initial connection, or a HELO or MAIL FROM:<> command was
550-rejected. Refusing MAIL FROM:<> does not help fight spam, disregards
550-RFC requirements, and stops you from receiving standard bounce
550-messages. This host does not accept mail from domains whose servers
550 Sender verify failed
Is it my Exchange server not verifying the user as valid to send because of the compuserve account?
Is it the customer's mail server not verifying the user as valid because it expects mail from compuserve?
Should/How do I set up a SMTP connector and does it leave me vulnerable to spam?
Any help would be grealty appreciated