I got some spam in my personal email account the other day so I took a look at the source to see if we are blocking the same type of mail when we encounter it (ie, is the mail actually the same or is this a new variation).
I was surprised to see that the mail client that the spammers were using was Outlook (or so claimed the headers). This caught be by surprise because I wouldn't have thought that Outlook could be used for spamming quite so easily - that is, I would have thought that spammers would generally use customized spamming software that sends out large volumes of mail. Outlook is more of a personal email client. I can think of a couple of possibilities:
1. The sending computer has been hijacked (the sending IP confirms this) and is sending spam out via spyware.
2. A spammer is using Outlook with a very large To: or CC: field.
3. A spammer built a plugin for Outlook to send large volumes of mail.
4. The Outlook header is fake - I tend to doubt this because the email contains a lot of HTML tags that Outlook typically inserts when it sends mail that other mail clients do not.
Whatever the case, I guess I still can come across new things here in the spam business. I thought I'd seen it all but the lesson is this - you can never see it all.