[exim] How to accept e-mail from a certain subnet even if AU…

Hi,

First let me explain what I am trying to do as this may be the entirely
wrong approach.

I have EXIM server setup for e-mail for a domain and it supports all the
usual stuff AUTH TLS e.t.c. On the network we have three networks the
internet itself, office network and guest network (10.10.100.0/24).
Everything is working fine for the domain and office network. However on
the guest network we can have various users where we have no control
over there PC's as they are guests, they are also not the most technical
people around so don't know the first thing about how there e-mail
clients are setup. So basically I want EXIM to listen for connections
from the 10.10.100.0/24 subnet and accept all attempts to relay the
guest mail regardless of whether the sending client uses NO AUTH, or is
set to AUTH, or is set to the TLS AUTH. This will only need to happen
for traffic on port 25, and for mail connections from the guest network.

I know you can turn off AUTH requirements for a subnet with
auth_advertise_host, but what I am not sure of is... If a client is set
to use AUTH and you don't advertise AUTH from the server...

1. Will the client still try to use AUTH, when it is not advertised?
2. If the client does try to use AUTH will the exim server jut ignore it
and accept the e-mail anyway or will it error?
3. Will this work if the client also uses TLS?

Finally am I on the right track for making this work, or do I need to
look to advertise AUTH and then just accept any credentials sent, as
long as the connection originates from the guest network. If this is the
approach how would I make exim accept any user password combination?

Thanks
Shane