Data Detectors allow you to turn addresses, phone numbers and dates in mail messages into Address Book contacts and iCal events. You can also turn selected text into to-do items or stickies.
To turn off Data Detectors, open the Terminal program from your Applications, Utilities folder, and type:
defaults write com.apple.mail DisableDataDetectors YES
To turn it back on again, type:
defaults write com.apple.mail DisableDataDetectors NO