This is a bit difficult to understand. I think there's two ways to interpret your question with two very different answers. I'll try to give both meanings I see and an answer to each question below.
1. Is there a setting I can choose on IIS's SMTP server (or any other mail
server for that matter) that will stop
other people marking email sent from my
server as junk.
No... There are things you can do with
DNS settings to manage email
reputation (spf, etc) but ultimately
this is a choice made by the
receiving server's operator, and also by their users.
2. Help, I think my server is being exploited by spammers, because the
legitimate mail I'm sending is being
rejected with messages that indicate I
have an open relay or am participating
in sending spam. What do I do?
In general terms, you need to make
- You are only accepting email
to send through this server from your
own internal processes... in other
words that your email server is
configured to only accept and forward
email from servers you control.
these processes are secure - there was
a spate of people exploiting issues in
email forms on webpages, for example,
to get around the problem I mention
- And any authentication you use
to connect from the process you want
to send email via this server hasn't