Why did a legitimate e-mail message get identified as spam?
There will be messages that you do not consider spam that the spam scanning service quarantines. There will also be messages that you consider spam that the spam scanning service allows through. The filter is trying to make a "best guess" at what could be spam and then provide a concise list to you in a timely fashion. This enables you to make a final decision as to whether you wish to receive the message.
In order to determine the reason for your messages being quarantined, you should release the desired message and look for the header and its corresponding information as documented in the FAQ item
How can I find out what led to a message being identified as spam
