I am running Exchange on an installation of SBS 2003 and I have recently run into a problem where random spam queues began showing up in my SMTP queues. I was first alerted to it because my antivirus software was telling me my server was infected, but luckily I think it's just because the spam contains malicious attachments. One weird thing is that all of the messages in the queue appear to be from 'email@example.com' to address on the spammer domain. Does this mean that they are trying to get me to email them sensitive information from my server? At any rate, I need to figure out how to secure my server so that the only people who can send email from my server are authenticated domain users. Does anyone know the best way to lock this down so that only domain accounts can send email, and no one else? Users need to be able to send mail both in and out of the office. Remote email is done through Remote Web Workplace and ActiveSync to smartphones. I am using the Microsoft-Server-ActiveSync web application in my default web site in IIS 6, in case that is providing any security holes for spammers to get through.
Any help is greatly appreciated.