Webmail and mail groups

Hello,I have a notes user that uses the client on his desktop when in the office, and webmail when out of the office. His problem is that he has a mail group that he created in his local address book. The group contains other notes users from our office as well as people from the outside. When he sends to the group using the client inside the building…everyone recieves his email. When he is outside the building using webmail only people from our office (in the group) will recieve the email and the outsiders do not. He gets an error mailed back to him saying the users somename@ourdomain.com does not exist. The email will put the outsiders name and also puts our domain after their name making it look like they are from our comapny.

Ideas? Hope I was clear enough. Thanks.