We have a distribution group setup on our SBS 2003 server, it has a an exchange email address and contains members from within the company, including a few contacts setup that have external addresses.
We then have a website setup to send to the email address of the distribution group, when a user fills in a form, an automated email with the form input is sent to this address, and then the group sends to some external contacts as well as the internal contacts.
When we use the site to email the distribution groups email address, the email goes through to the internal users fine, but looking in Exchange message tracking, just after it gets to the "SMTP: Message Routed and Queued for Remote Delivery" part, I see a message saying a Non-delivery report has been generated.
The problem seemed to be resolved when going to "Exchange System Manager" > "Connectors" > "Relay to External Contacts" and adding the external domain to the "Address space" tab (I believe I must do this because the website is not sending any authentication details to the server and is just simply emailing an address).
I was told by a colleague that this is a bad idea as it can open up the server as a spam relay for that domain, he explained that should a spammer discover that it is a relay for that domain, they can freely send whatever they like.
I have been Googling but I can't find anything related to this. Can anyone tell me if there is a risk of spam if I add the external domains to the "Address space" tab under "Relay to External Contacts"?
Thanks in advance & apologies if this is the incorrect stack site to ask this question.