let me give you the set up.
We have an internal machine that has WAMP server 2.0 installed with php, mysql etc. On here I have created a php order system that we can keep track of orders currently awaiting. When we order something it sends an email to the supplier.
The problem is that when I process the order and try and send an email I get an error back saying
Warning: mail() [function.mail]: SMTP server response: 550 5.7.1 Unable to relay in file.php on line 22
in the php ini file it is set up to find the exchange server
SMTP = 172.16.0.1
smtp_port = 25
And this works perfectly when sending an email to a user who is on our exchange server. The problem happens when trying to send an email to an external address. One that is not part of our domain.
I think it might be to do with authentication but am not sure how to configure this. So if anyone can help that would be great.