Here is the picture :

I have a main mail server1 (sendmail 8.13) which works fine, and for some users has a .forward file for server2 (also sendmail 8.13).
On server2 I set up SMTP AUTH and it works beautifully, BUT it asks EVERYBODY to authenticate, also my server1. So server1 can not forward mail to server2.

I have Googled for quite some time, and have found no instance/example/anything to suggest how can I make a exception for server1 on my server2, so that it is not asked for authentication.

Help please!