in other words, it starts with [NEW], ends with [PM]
then it is a forum notification. You subscribed to receive forum notification every time someone posts a new message into some forum or into some thread.
To unsubscribe notifications, click on the [PM] part.
[PM] is linked to the Private Message, and Private Message contains a link to the unsubscription page.
[NEW] is linked directly to the forum message.
If you are a forum moderator, you may be getting messages that look like this:
[Bad Alert] Re: Racism is evil and wrong no matter what form it takes by Count Blah [PM]
If yes, it is because it is an alert sent to you from a forum reader. There are 2 kinds of alerts. Good alert and bad alert.