If you have two servers you can also accomplish what you want.
The first server is pretty much a normal NetaMail server that supports all of your users. It uses the PlusPack to keep a group of users from sending outbound messages.
The second server 'front-ends' the first server, meaning that the DNS MX record for the domain points to this server and it selectively forwards to the second server. The filtering could be accomplished several different ways. The alias agent running on this machine could be configured to send messages addressed to these folks to a junk mailbox. If you want the messages to bounce, you could alias them from <real username> to UnknownUser. You could also set up rules for these users to that the rules sever would eat messages addressed to them. You could configure these users to have an auto reply that says this user can not be reached or does not exist. You could also configure your domain on this server as a ETRN domain and have the alias agent change messages addressed to the 'haves' to the hostname of the second machine, from <real username>@<your domain> to <real username>@<hostname of server 1>.
There are a several resources for NetMail administrators where you get ideas. If you are not already subscribed to nimstalk@nimsinfo.com, there are hundreds of administrators like your self out there sharing ideas and solving technical issues. There are also the NetMail forum on support.novell.com/forums/.

What's New in NetMail 3.5?
Question: Where can I find a list of the new features in NetMail 3.5?
Answer: Here's a quick overview of the new features in the NetMail 3.5 online documentation. http://www.novell.com/coolsolutions/netmail/features/a_whats_new_in_netmail35_nm.html.

RBL Lists
Question: Where can I find out if a server has been blacklisted?
Answer: Here are a few sites that were mentioned in the NetMail Forum. If you have other suggestions, please send them to: netmailmag@novell.com and we'll add them to the list.

NetMail for NT
Question: I am trying an evaluation copy of NetMail for NT. I have asked several people at Novell how to change the license file without reinstalling the product to go to a licensed version.
The questions in your FAQ's are not related to NT. The eval license file is just a file named "version".
Answer: NetMail uses the license file NetMail.nlf which is found in the bin directory. Just get the license file from the full product and replace the current file in the bin directory. On Windows it is just as easy to install over the top, no setting will be erased by installing over an eval version.

Notify program for NetMail?
Question: Is there a notifiction program for NetMail?
Answer: Check out the following third party products that will notify you when you receive new mail.
- NetMail Notify: Omni Technology Solutions Inc
- MyRealBox Notifier: P&H Developments Limited
- NMBuddy: P&H Developments Limited

Modify WebAccess Template
Question: I would like to modify the WebAccess template for NetMail 3.1. Is there any documentation on how to do this?
Answer: The NetMail SDK (3 April 2003) is available on Novell's Developer Leading Edge site.
The SDK includes documentation and usable sample code for the Networked Messaging Application Protocol (NMAP). NMAP provides full control over the NetMail queuing system and full access to the message store.
The SDK also includes ModWeb documentation. ModWeb is a template-based, self-contained Web engine that eliminates the need for JVMs, servlet gateways, and CGI scripts in an HTML environment.
Download the NetMail SDK here: http://developer.novell.com/ndk/leadedgebydate.htm Also, check out the NetMail FAQ: http://www.novell.com/coolsolutions/netmail/features/a_nims_faq_nm.html.

Converting Netmail Evaluation to Licensed Copy
Question: After installing the evaluation version and then buying the full version of NetMail, is there a way to replace the eval version with minimum effort to the licensed version without doing a full reinstall?
Answer: You can use your existing install. In the purchased version, look for the file "netmail.nlf" and copy it to your sys:system folder.

Configuring a POP Client
Question: I don't understand the setup for the pop e-mail. In the proxy configuration, under preferences, what do I put in Host? Username? Password? Type? Leave?
Answer: Check out this article for instructions on how to set up NetMail to retrieve messages from your other accounts. Collecting Messages From Other E-mail Accounts.
