I think that the problem is a bad mail program at your clients, A user should not see the 250 status, it is not a failure of any sort but I have seen it as a return status sent to a user.
Here is an example that I have seen from someone who sent us a message. The message failed and this is the status that they received: Reporting-MTA: dns; toq7.bellnexxia.net Arrival-Date: Fri, 20 Jul 2007 21:26:11 -0400 Received-From-MTA: dns; Christine (64.230.70.248) Content-Type: text/plain Final-Recipient: RFC822; <[EMAIL PROTECTED]> Action: failed Status: 4.4.7 Remote-MTA: dns; thinkage.ca Diagnostic-Code: smtp; 250 This is hurting you more than it is hurting me.