Alexandre, To answer your first question, yes we filter outbound mail. We were once in the same position as you are now and corrected the problem successfully. All the advice given is good and I can attest that it will work.
We first created a separate outbound service with authenticated smtps added and then worked hard to convert all clients to the new service. We went so far as to make it mandatory that all new clients were only allowed to send mail if authenticated. Our support staff would change a users MUA to authenticated connection if the client called support for *any* reason. We filter all messages at connection time and refuse the message if it scores above the set SpamAssassin limit or contains a virus. The user knows immediately their mail will not go out. When the client calls support, the first thing support does is of course, change their MUA to authenticated smtps. We rate limit all outbound mail, exceed the messages per minute and we block your connection until a sysadmin looks at the problem. We limited recipients per message, first at 100, then we moved to 75, now we are 50. Want more recipients? Purchase a mail list with verp from us. A few complaints, a few clients changed to another provider, but the problem stopped. We have feedback loops setup and we read the messages everyday. We have all our hosted domains postmaster mail sent to us, and we read it everyday. We spot a problem and we have the client on the phone within minutes. We have had to block a few clients until they cleaned up their network/PC, but not very often anymore. We now have *all* (100% except Nagios alerts) mail traffic flowing through our filtered outbound servers. Clients, office, printers, scan2mail, fax2mail, even the web servers use our outbound servers as smart hosts. Messages go through our outbound servers, or they do not leave our network. We are not perfect, we still see some feedback (mostly bad addresses and clueless recipients) but we are far better than we were four years ago. Listen to what the experts are telling you and implement their suggestions. You may loose a client or two, but you will improve your network and get better clients in return for your efforts. DAve -- "Posterity, you will know how much it cost the present generation to preserve your freedom. I hope you will make good use of it. If you do not, I shall repent in heaven that ever I took half the pains to preserve it." John Adams http://appleseedinfo.org
