I'd completely forgotten that Postfix Enabler also installed a little utility called Anomy for helping to filter email. I'd forgotten until I had to troubleshoot a problem that was effecting some mail my wife was receiving and it brought up a problem I'd forgotten about...
Anomy has the ability to 'defang' parts of HTML code embedded in messages, usually this will keep rogue code from executing on your machine, but in this case was effecting how mail messages were being displayed.
I'd first noticed this when I was forwarding a certain email back to myself, the quoted section had several zeros on there that I couldn't figure where they came from. Eventually I discovered that this was some oddity in the HTML formatting, so I just turned that off in Mail (OS X's mail application) and forgot about it.
Today, my wife received a mail with several numbers at the start from someone who's mailed her before, and she never saw anything like that. After scratching my head then looking at the raw source of the message, things finally started clicking.
I need to dig into this a bit further, but I'm thinking with all the other spam filtering I'm doing, I should be safe to just disable this feature in Anomy, it's a quick fix, just change the following in the anomy.conf file:
feat_html = 1
feat_html = 0
That should do it! I'll investigate more and see what else I can find out about this problem. I figured it was easier to deactivate this one setting than to try removing Anomy itself.