Hello, and welcome to the Vista Forums!
I see your problem. This is being rejected because of Heuristics, rather than a database, and so false positives are being generated. Technically speaking, this is not a true false positive, but it does not really matter to you whether it is or not!
Right, this error is being generated because there is a URL concealment in your newsletter, which could be a phishing attack, and so is being blocked. There are two ways to fix this, remove the URL concealment, or completely disable the Heuristics Scanning of URLs. Ideally, we would change the newsletter, as the Heuristics will pick up some real phising attacks, which we would want blocked.
The most common cause of this error message is a TinyURL link, as I cannot see where it is leading me to, without a lot of analysis, which the average user would not do. You could be leading me anywhere, to the worst sorts of websites, and I would just blindly stumble into it. I understand that you are not doing this, but do you see the problem, and why this has been flagged up as a safely issue?
So, please remove all TinyURLs, and replace them with the actual URLs, and this Newsletter should be allowed through. Failing that, we could completely disable this protection (not recommended) and may be blocked at the receiving end, or (if applicable) you could get this newsletter to me, and I could have a look, and see if I could find the fault.
I don't know how you want to work this, but could you please give a bit of feedback on if you find anything that might be classed as dodgy, such as TinyURLs?