Our sister company which is not on our network and does not use exchange is having trouble sending us email. They do not have any trouble sending email to anyone else. The minute they send the email it comes back with a failure notice which I have attached to this post. We can send them email and they receive it with no problems. I am not very strong with exchange and it was set up before I took this position. The exchange 2000 is part of SBS 2003 and as far as I can tell has a basic configuration. We do not run any third party filtering device or software. I am really at a wall here and do not know where to go from here. To make matters worse I am not even sure if it is on our end, the site that handles our sister companies email imitate response is that it is not on their end. Please help.