What's in Your Inbox?

I get a lot of email--about 25,000 messages per month. Not surprisingly, the bulk of the messages are spam. Because Windows IT Pro has made my email address public for years, I receive most every spam message and email virus that makes the rounds. As such, I have a pretty stringent filtering system on my main email client computer. I use Microsoft Office Outlook 2003's Junk E-mail Filter and a third-party mail-filtering tool, along with a series of rules that sort my mail into various folders. Over time, I've fine tuned the system so that I no longer check the Junk folder, which contains the most egregious junk mail, and check my Spam folder daily, which is split about 50/50 between more clever spam and informational messages from various services or marketing people but rarely has more than 25 messages on any given day. My Inbox almost never contains anything that doesn't belong.You can imagine my surprise last week when I checked my Inbox and found more than 900 messages that my junk mail filters should have caught. After spending about an hour separating the wheat from the chaff, I was able to devote my attention to determining what had caused the breakdown in my carefully crafted junk email defenses.I looked at my email rules and found no problems, so I checked the third-party spam-filtering application. I was running the most recent version, and when I sent myself mail to that account from an account identified as a spam sender, the application dealt with the message appropriately.This left only Outlook's Junk E-mail Filter as the possible culprit. A quick check of the Office Update Web site confirmed that I was running the most recent version of Outlook with all applicable patches applied. It was time to look for more subtle problems.A glance at Outlook's folder view of my email provided the answer: My Junk folder contained 65,536 messages. Every now and then I scan the headers of the messages in the Junk folder to make sure I haven't filtered out anything important before I manually empty the folder. It had been about 10 weeks since I last cleared out the Junk folder, and the fact that the number of messages in the folder was exactly 65,536 assured me that I had found the problem.I emptied the Junk folder and voila; my junk filters began working again. So how did I know that the number of messages was the problem? The number 65,536 is 1024 x 64 or 64K. Whoever coded the junk filter feature in Outlook determined that the Junk folder would never contain more than 65,536 junk messages, and as a result, once the emails in the folder reached that number, the filters stopped working.It's unfortunate that a filtering service isn't safe with a limit of 65,000 junk messages, from both the perspective of the amount of junk mail being sent across the Internet and of the development choice to allow only that many messages in the folder; However, the problem is unlikely to be concern with typical email Inboxes.