emails not sent after new account creation

I've installed MS2 Max v 1.5. Accounts create ok but emails won't go through - always come back to me as undeliverable. The email address the message is being sent to is correct and I've tried all combinations of settings in the admin area with regard to email options. Running on Unix system, shared server but no SSL setup due to just testing this out.

Here's error message (I've put in dummy emails and server names but these are all correct in original message):

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:

(CorrectAddress@domain.com
SMTP error from remote mailer after RCPT TO:<CorrectAddress@domain.com>:
host domain.com [xxx.xx.xx.x]: 550-Verification failed for <adminEmail@domain.com>
550-Unrouteable address
550 Sender verify failed

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

Return-path: <adminEmail@domain.com>
Received: from nobody by servername.com with local (Exim 4.24)
id 1ANxnS-0004TB-1K
for CorrectAddress@domain.com; Sun, 23 Nov 2003 10:13:18 -0700
To: "customer name" <CorrectAddress@domain.com>
Subject: Welcome to osCommerce etc.

Thanks if anyone can help.

got the problem fixed. wasn't with osCommerce; problem was with web hosting service