I have an internal SMTP IIS Server that I use to send out emails to customers as well as send internal reports to users and distribution groups. Before we upgraded to SP1 we were able to send to distribution groups and customers without issues. Now when we send internal emails via SMTP to a distribution group we get an error that the email is not authenticated and has been blocked.
Now before you tell me untick the require authentication or allow external users to send to the distribution group anonymously know that I cannot allow external emails to this group. Another thing is the SMTP server is authenticated and sends anonymous emails to distribution groups.
I would like to know how do I send to a distribution group from my internal SMTP without allowing external email to the distribution group?